Vertical solid-state devices

ABSTRACT

An optoelectronic device comprising a pad substrate comprising an array of pads connected to a driving circuit; and a device layer structure deposited on a substrate, wherein the device layer structure including a plurality of active layers and conductive layers; and a pillar layer formed on or part of a first conductive layer, wherein the pillar layer is patterned into array of pillars to create pixelated micro devices and wherein the array of pillars is bonded to the array of pads. The redundant pillars that are not bonded to the array of pads may be provided a fixed voltage or used as sensors.

BACKGROUND AND FIELD OF THE INVENTION

The present invention relates to vertical solid-state devices, lateralconduction manipulation of vertical solid state devices, and methods ofmanufacture thereof. The present invention also relates to thefabrication of an integrated array of micro devices, defined by an arrayof contacts on a device substrate or a system substrate.

Integrating micro optoelectronic devices into a system substrate mayresult in high performance and high functionality systems. However, toreduce the cost to create higher pixel density devices, the size of theoptoelectronic devices should be reduced. Examples of optoelectronicdevices are sensors and light emitting devices, such as light emittingdiodes (LEDs). As the size of the optoelectronic devices is reduced,however, device performance may start to suffer. Some reasons forreduced performance include higher leakage current due to defects,charge crowding at interfaces, imbalance charge, and unwantedrecombination such as auger and nonradiative recombination.

LEDs and LED arrays may be categorized as vertical solid-state devices.Micro devices may be sensors, LEDs or any other solid devices grown,deposited, or monolithically fabricated on a substrate. The substratemay be the native substrate of the device layers or a receiversubstrate, onto which device layers or solid-state devices aretransferred.

Various transferring and bonding methods may be used to transfer andbond device layers to the system substrate. In one example, heat andpressure may be used to bond device layers to a system substrate. In avertical solid-state device, the current flowing in the verticaldirection predominantly defines the functionality of the device.

Patterning LEDs into micro size devices to create an array of LEDs fordisplay applications comes with several issues including materialutilization, limited PPI, and defect creation.

An object of the present invention is to overcome the shortcomings ofprior art by providing improved vertical solid-state devices.

This background information is provided for the purpose of making knowninformation believed by the applicant to be of possible relevance to thepresent invention. No admission is necessarily intended, nor should beconstrued, that any of the preceding information constitutes prior artagainst the present invention.

SUMMARY OF THE INVENTION

According to one embodiment, an optoelectronic device comprising a padsubstrate comprising an array of pads connected to a driving circuit; adevice layer structure deposited on a substrate, wherein the devicelayer structure including a plurality of active layers and conductivelayers; and a pillar layer formed on or part of a first conductivelayer, wherein the pillar layer is patterned into array of pillars tocreate pixelated micro devices and wherein the array of pillars isbonded to the array of pads.

According to one embodiment, a method of fabricating an optoelectronicdevice comprising forming a device layer structure, including aplurality of active layers and conductive layers, on a substrate,forming a pillar layer on at least a part of a first conductive layer,wherein the pillar layer is patterned into array of pillars to createpixelated micro devices; and bonding a pad substrate comprising an arrayof pads connected to a driving circuit, to a top surface of the array ofpillars.

The foregoing and additional aspects and embodiments of the presentdisclosure will be apparent to those of ordinary skill in the art inview of the detailed description of various embodiments and/or aspects,which are made with reference to the drawings, a brief description ofwhich is provided next.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other advantages of the disclosure will becomeapparent upon reading the following detailed description and uponreference to the drawings.

FIG. 1A illustrates an optoelectronic device with at least twoterminals.

FIG. 1B illustrates an optoelectronic device with an MIS structure on atleast one side of the device.

FIG. 1B-1 shows an example of an optoelectronic device with an MISstructure on at least one side of the device.

FIG. 10 illustrates a top view of the optoelectronic device in FIG. 1Bwith MIS structures on all sides.

FIG. 2A illustrates an exemplary embodiment of a process to form an MISstructure on an optoelectronic device prior to a transfer process.

FIG. 2B illustrates an exemplary embodiment of a process to form an MISstructure on optoelectronic devices both prior to and after the transferprocess.

FIG. 2C illustrates an exemplary embodiment of a process to form an MISstructure on an optoelectronic device after the transfer process.

FIG. 3 illustrates transferred micro devices with a negative slope on asystem substrate.

FIG. 4 illustrates a process flow chart of a wafer etching process formesa structure formation.

FIG. 5A illustrates a transferred micro device with a positive slope onthe system substrate.

FIG. 5B illustrates the formation of different MIS structures ontransferred micro devices.

FIG. 5C illustrates the formation of a passivation or planarizationlayer, and the patterning of the passivation or planarization layer tocreate openings for electrode connections.

FIG. 5D illustrates the deposition of electrodes on the micro devices.

FIG. 6A illustrates embodiments for the formation of different MISstructures on micro devices before the transfer process.

FIG. 6B illustrates micro devices with MIS structures transferred onto asystem substrate, and different means to couple the devices and MISstructures to electrodes or a circuit layer.

FIG. 6C illustrates micro devices with MIS structures transferred onto asystem substrate and different means to couple the devices and MISstructures to electrodes or a circuit layer.

FIG. 7A illustrates another embodiment of the formation of different MISstructures on micro devices before the transfer process.

FIG. 7B illustrates micro devices with MIS structures transferred onto asystem substrate and different means to couple the devices and MISstructures to electrodes or a circuit layer.

FIG. 8A illustrates a schematic of a vertical solid-state micro deviceshowing the lateral current components and partially etched top layer.

FIG. 8B illustrates a side view of an array of micro devices including adevice layer with a partially etched top layer and top layer modulation.

FIG. 8C illustrates a side view of an array of micro devices including adevice layer with a top conductive modulation layer.

FIG. 8D illustrates a side view of an array of micro devices including adevice layer with nanowire structures.

FIG. 8E illustrates a cross section of an MIS structure surrounding acontact layer.

FIG. 8F illustrates a side view of an array of micro devices includingcontacts separated by dielectric or bonding layers.

FIG. 8G illustrates a side view of an array of micro devices includingcontacts separated by dielectric or bonding layers.

FIG. 9A illustrates a side view of a conventional Gallium nitride (GaN)LED device.

FIG. 9B illustrates a fabrication process of an LED display and anintegration process of a device substrate with micro devices defined bytop contacts and bonding the substrate to a system substrate.

FIG. 9C illustrates an LED wafer structure including an array of microdevices defined by the top contact.

FIG. 9D illustrates an LED wafer structure including an array of microdevices defined by the top contact and partially etched top conductivelayer.

FIG. 9E illustrates an LED wafer structure including an array of microdevices defined by the top contact and a laser-etched top conductivelayer.

FIG. 9F illustrates an LED wafer including an array of micro devicesbonded to a backplane structure.

FIG. 9G illustrates an LED wafer including an array of micro devicesbonded to a backplane structure with a common top electrode.

FIG. 10A illustrates an LED wafer including an array of micro devicesbonded to a backplane structure with a common transparent top electrode.

FIG. 10B illustrates an integrated LED wafer bonded to a systemsubstrate and includes an array of micro devices defined by topcontacts.

FIG. 10C illustrates an LED wafer with a buffer layer and metalliccontact vias.

FIG. 10D illustrates an LED wafer including an array of micro deviceswith a patterned top conductive layer.

FIG. 10E illustrates an integrated device substrate with micro devicesdefined by top contacts bonded to a system substrate.

FIG. 10F illustrates an integrated device substrate with micro devicesdefined by top contacts bonded to a system substrate, and opticalelements formed between adjacent micro devices.

FIG. 10G illustrates a transferred LED wafer including an array of microdevices with a patterned top conductive layer and light managementscheme.

FIG. 10H illustrates a transferred LED wafer including an array of microdevices with a patterned top conductive layer and light managementscheme.

FIG. 10I illustrates a transferred LED wafer including an array of microdevices with a patterned top conductive layer and light managementscheme.

FIG. 10J illustrates a transferred LED wafer including an array of microdevices with a patterned top conductive layer and light managementscheme.

FIG. 10K illustrates a transferred LED wafer including an array of microdevices with a patterned top conductive layer and light managementscheme.

FIG. 10L illustrates stacked devices with isolation methods.

FIGS. 11A and 11B illustrate an integration process of a devicesubstrate and a system substrate.

FIGS. 12A to 12D illustrate an integration process of a device substrateand a system substrate.

FIGS. 13A and 13B illustrate an integration process of a devicesubstrate and a system substrate.

FIGS. 14A to 14C illustrate an integration process of a device substrateand a system substrate.

FIGS. 15A to 15C illustrate an integration process of a device substrateand a system substrate.

FIG. 16A illustrates a device with dielectric layer deposition on thewafer surface.

FIG. 16B illustrates a device with a dielectric layer etched to createan opening on the layer for subsequent wafer etching.

FIG. 16C illustrates mesa structures after a wafer substrate etchingstep.

FIG. 17 illustrates a process flow chart for forming an MIS structure.

FIG. 18A illustrates a dielectric and metal layer deposited on a mesastructure to form an MIS structure.

FIG. 18B illustrates a wafer with a pattern formed using aphotolithography step.

FIG. 18C illustrates a wafer with a dielectric layer dry-etched usingfluorine chemistry.

FIG. 18D illustrates a wafer with a second dielectric layer.

FIG. 18E illustrates a wafer with an ohmic contact.

FIG. 19 illustrates a schematic diagram of a floating gate for biasingthe walls of a semiconductor device.

FIG. 20 illustrates a semiconductor device including a floating gate forbiasing the walls of the semiconductor device.

FIG. 21 illustrates an exemplary flowchart of developing a floatinggate.

FIG. 22 illustrates a semiconductor device and a method of charging thefloating gate.

FIG. 23 illustrates another exemplary structure of a floating gate tobias the walls of a semiconductor device.

FIG. 24 illustrates another exemplary embodiment to bias the walls of asemiconductor device.

FIG. 25A illustrates a side view of another embodiment of an MISstructure.

FIG. 25B shows another embodiment for a vertical device with a differentpad configuration.

FIG. 25C illustrates another exemplary embodiment for a vertical devicewith an MIS structure.

FIG. 25D illustrates another embodiment for a vertical device with adifferent pad configuration.

FIG. 25E illustrates a side view of another embodiment of an MISstructure.

FIG. 25F shows another embodiment for vertical devices with an MISstructure with pads on both sides.

FIG. 26A illustrates a top view of the MIS structure of FIG. 25A.

FIG. 26B illustrates a top view of another embodiment of an MISstructure.

FIG. 26C illustrates a top view of another embodiment of an MISstructure.

FIG. 26D illustrates a top view for a vertical device with an MISstructure.

FIG. 26E illustrates a top view for the vertical device with an MISstructure.

FIGS. 27A to 27C illustrate a fabrication process of an LED display andintegration process of a device substrate with micro devices defined bytop contacts and bonding the substrate to a system substrate.

FIGS. 28A to 28D illustrate a fabrication process of an LED display andintegration process of a device substrate with micro devices defined bytop contacts and bonding the substrate to a system substrate.

FIGS. 29A to 29D illustrate a fabrication process of an LED display andintegration process of a device substrate with micro devices defined bytop contacts and bonding the substrate to a system substrate.

FIGS. 30A to 30B illustrate a fabrication process of an LED display andintegration process of a device substrate with micro devices defined bytop contacts and bonding the substrate to a system substrate.

Use of the same reference numbers in different figures indicates similaror identical elements.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and will be described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure covers all modifications, equivalents, and alternativesfalling within the spirit of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION

While the present teachings are described in conjunction with variousembodiments and examples, it is not intended that the present teachingsbe limited to such embodiments. On the contrary, the present teachingsencompass various alternatives and equivalents, as will be appreciatedby those of skill in the art.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

As used in the specification and claims, the singular forms “a”, “an”and “the” include plural references unless the context clearly dictatesotherwise.

The term “comprising” as used herein will be understood to mean that thelist following is non-exhaustive and may or may not include any otheradditional suitable items, for example one or more further feature(s),component(s) and/or element(s) as appropriate.

The terms “device” and “micro device” and “optoelectronic device” areused herein interchangeably. It would be clear to one skilled in the artthat the embodiments described here are independent of the device size.

The terms “donor substrate” and “temporal substrate” are used hereininterchangeably. However, it is clear to one skilled in the art that theembodiments described herein are independent of the substrate.

The terms “system substrate” and “receiver substrate” are used hereininterchangeably. However, it is clear to one skilled in the art that theembodiments described here are independent of substrate type.

The present disclosure relates to methods for lateral conductionmanipulation of vertical solid state devices, particularlyoptoelectronic devices. More specifically, the present disclosurerelates to micro or nano-optoelectronic devices in which deviceperformance is being affected by size reduction. Also, described is amethod to create an array of vertical devices by modifying the lateralconduction without isolating the active layers. Also, disclosed is anarray of LEDs using vertical conductivity engineering to enable currenttransport in a horizontal direction and control to the pixel area, sothere is no need to pattern the LEDs.

Herein also is described a method of LED structure modification tosimplify the integration of monolithic LED devices with backplanecircuitry in an LED display while preserving device efficiency anduniformity. The present methods and resulting structures increase thenumber of LED devices fabricated within a limited wafer area and mayresult in lower fabrication cost, decrease the number of fabricationsteps, and provide higher resolution and brightness for LED displays.LED devices in a substrate may be bonded to an electronic backplane,which drives the devices or pixels in a passive or active manner.Although the following methods are explained with one type of LEDdevice, they can be easily used with other LED and non-LED verticaldevices, such as sensors. LED devices in a substrate as herein describedmay be bonded to an electronic backplane which drives these devices(i.e., pixels) in a passive or active manner.

Also described herein is a method to improve the performance of anoptoelectronic device by manipulating the internal electrical field ofthe device. In particular, limiting the lateral current flow of verticalsolid-state devices may improve the performance of the devices. Inparticular, diverging current from the perimeter of a vertical devicemay be accomplished by modifying the lateral conduction. The resistanceof the conductive layers may be modified by oxidation, and the lateralresistance of the conductive layers may be modified by modifying thebias condition. A contact can also be used as a mask to modify thelateral resistance of the conductive layer. The present devices may alsohave conductive layers on the sides and functional layers in the middle.

Also provided is a method of pixelating a display device by defining thepixel pad connection in a backplane and attaching the LED device withvertical conduction modulation to the backplane. In one embodiment, thecurrent spreader may be removed, or its thickness may be reduced tomodulate the vertical conduction. In another embodiment, some of themicro device layers may be etched to create vertical conductionmodulation. A bonding element may be used to hold the device to thebackplane. Structures and methods are described to define micro deviceson a device layer by forming contact pads on the device layer beforetransferring the device layer to a receiver substrate. Also describedare structures and methods to define the micro devices by contact padsor bumps on the receiver substrate in an integrated micro device arraysystem comprising a transferred monolithic array of micro devices and asystem substrate.

Also described are methods to manipulate the top conductive layer of avertical device in which the functionality of the device predominantlyis defined by the vertical currents. In one embodiment the methodcomprises: top layer resistance engineering in which the lateralresistance of the top layer may be manipulated by changing the thicknessor specific resistivity of the top layer; full or partial etchingmodulation in which the top layer of the vertical device may bemodulated by any means of etching; and material conductivity modulationin which the resistance of the top layer may be modulated by variousmethods including but not limited to etching, counter doping, and laserablation. The contact pads on the top device layer may define the sizeof the individual micro devices. After transferring micro devices, acommon electrode may be deposited on the transferred monolithic array ofmicro devices to improve the conductivity. The common electrodes may beformed through vias in the top buffer or dielectric layers transferredor deposited on the monolithic array of micro devices. Also, the toplayer of the transferred monolithic array of micro devices may bemodulated by any removal means. In this case, optical elements may beformed in the removed regions of the modulated top layer.

Also described is a method to form an array of micro devices on anintegrated structure in which the device layer, prepared according tothe aforementioned methods, is transferred to a receiving substratewherein the contact pads on the top of the receiving substrate may bebonded to the device layer and the size of the individual micro devicesmay be defined partially by the size of the contact pads or bumps on thereceiver substrate. Spacers or banks may be formed around contact padsor bumps to fully define the size of the micro devices. The spacers orbanks around contact pads or bumps may be adhesives to promote bondingthe device layer to the receiver substrate. The top layer of theintegrated micro device array may be modulated by any means of removing.In one embodiment, the optical elements may be formed in the removedregions of the modulated top layer.

In an embodiment, the at least one MIS structure may be formed with oneof the device faces as the semiconductor layer. The structure may beused to manipulate the device's internal electrical field to control thecharge transition and accumulation. The MIS structure may be formedprior to moving the device into the system substrate, or after thedevice is formed into the system substrate. The electrode in the MISstructure may be transparent to let the light pass through, or theelectrode may be reflective or opaque to control the direction of thelight. Preferably, the device output comprises visible light to createan array of pixels in a display. The electrode in the MIS structure maybe shared with one of the device's functional electrodes. The electrodein the MIS structure may also have a separate bias point. The input oroutput of the micro devices may be any form of electromagnetic wave.Non-limiting examples of the device are an LED and a sensor. Structuresand methods to improve micro optoelectronic devices are also describedherein. The device performance may be improved by manipulating theinternal electric field. In one case, the MIS structure is used tomodulate the internal electrical field.

In micro device system integration, devices may be fabricated in theirnative ambient conditions, and may be then transferred to a systemsubstrate. To pack more micro devices in a system substrate or reducethe cost of material, the size of micro devices may be as small aspossible. In one example, the micro devices may be 25 μm or smaller andin another example 5 μm or smaller. As the original devices and layerson the donor substrate are being patterned to a smaller area, theleakage and other effects increase which reduces the performance of thedevices. Although passivation may improve the performance to someextent, it cannot address other issues such as non-radiativerecombination.

Another embodiment is an optoelectronic micro device where it consistsof first and second conductive layers, active layers between said firstand second conductive layers, contacts to the first and secondconductive layers on the same surface, metal-insulator-semiconductorformed between at least one of conductive or active layers and a gateelectrode and a dielectric layer to separate the contact to the saidgate electrode and one of the conductive layer.

Various embodiments in accordance with the present structures andprocesses provided are described below in detail.

Vertical Devices with Metal-insulator-Semiconductor (MIS) Structures

Described is the use of an MIS structure to modulate the internalelectric field of a vertical device to reduce the unwanted effectscaused by size reduction. In one embodiment, the structure is fullyformed on the devices in the donor or temporal substrate and then movedto the system substrate. In another case, the MIS structure is formed onthe devices integrated on the receiver or system substrate. In anothercase, the MIS structure is formed partially on the devices prior tobeing integrated into the receiver substrate, and the MIS structure iscompleted after transferring the device into the receiver substrate.

The system substrate may be any substrate and may be rigid or flexible.The system substrate may be made of glass, silicon, plastics, or anyother commonly used material. The system substrate may also have activeelectronic components, such as but not limited to transistors,resistors, capacitors, or any other electronic component commonly usedin a system substrate. In some cases, the system substrate may be asubstrate with electrical signal rows and columns. In one example, thedevice substrate may be a sapphire substrate with LED layers grownmonolithically thereon, and the system substrate may be a backplane withcircuitry to derive micro-LED devices. As part of the vertical devices,MIS structures may be formed from a layer of metal, a layer ofinsulating material, and a layer of semiconductor material.

With reference to FIG. 1A, a micro device 100 includes two functionalcontacts A 102 and B 104. Biasing the micro device 100 causes a current106 to flow through the bulk of the micro device 100. For light emittingdevices, the charges recombine in light emitting layer(s) and createphotons. For sensing devices, the external stimulation (e.g., light,chemical, Tera Hz, X-ray) modulates the current. However, non-idealitiesmay affect the efficiency of the micro device 100 in both cases. Oneexample is the leakage current 108 mainly caused by the defects in thesidewalls. Other non-idealities may be non-radiative recombination, suchas auger recombination, charge crowding, or charge imbalance. Theseissues become more dominant as the size of the device is reduced.

With reference to FIG. 1B, the micro device 100 further includes an MISstructure 110 to modulate the internal field and reduce some of theaforementioned issues. At least one MIS structure 110 is formed on oneof the faces of the micro device 100. The MIS structure 110 is biasedthrough an electrode 112. If the MIS structure 110 is formed on morethan one surface of the micro device 100, it can be a continuousstructure or a few separate MIS structures. The electrodes 112 can beconnected to the same biases for all faces or different biases. The MISstructure can be on different sides of the device to improve performanceor offer different functionality.

FIG. 1B-1 shows another exemplary structure with different MIS structurepossibilities. The MIS structure 110 on the same side as the deviceelectrodes (102, 104) can control the flow of the current from theelectrodes (102, 104) to the edge sides, while other MIS structures onthe sides with no device electrode can confine the charges and alsocontrol the flow of the current. A device may use one or more of theseMIS structures 110. At least two of the MIS structures 110 on differentsides of the device may have the same electrode.

In an exemplary embodiment illustrated in FIG. 1C, the MIS structure 110surrounds the micro device 100 in one continuous form on or around aplurality of faces of the micro device 100. Applying bias to the MISstructure 110 may reduce the leakage current 108 and/or avoid bandbending under high current density to avoid non-radiative recombinationand/or assist one of the charges to enhance the charge balance and avoidcurrent crowding. The biasing conditions may be chosen to fix thedominant issue. For example, in the case of a red LED, leakage currentis the major source of efficiency loss at moderate to low currentdensities. In this case, the biasing condition may block/reduce theleakage current to allow a significant efficiency boost. In anothercase, such as a green LED, Auger recombination may be the main issue.The biasing condition may be adjusted to reduce this type ofrecombination. It is noted that one bias condition may eliminate/reducemore than other bias conditions and LED types. Dynamically adjusting thebiasing condition may also provide better performance. For example, inlower current density, one effect, such as leakage current may be thedominant effect, but at a higher current density, charge crowding, andother issues may be the dominant effect. As such, the bias may bemodified accordingly to offer better performance. The bias may beadjusted as a single device, cluster of devices, or the entire array ofdevices. The bias may also be different for different devices. Forexample, LED versus sensors, or red versus green LEDs may all havedifferent biasing conditions.

The process to form the MIS structure 112 on the micro device 100 isdescribed in FIGS. 2A to 2C. The order of the steps in these processesmay be changed without affecting the final results. Moreover, each stepmay be a combination of a few smaller steps.

With reference to FIG. 2A, in a first step 200, the micro devices 100are formed. During step 200, the micro devices 100 are formed by eitherpatterning or selective growth. During step 202 the micro devices 100are prepared for transfer which may include cleaning or moving to atemporary substrate. During step 204, the MIS structure 112 is formed onone surface of the micro device 100. During step 206, the device 100 isagain prepared for transfer, which may include a lift-off process, acleaning process, and/or other steps. In addition, during step 206,connection pads or electrodes for device function electrodes or for theMIS structure 112 may be deposited and/or patterned. During step 208,selected devices 100 are transferred to a receiver substrate by variousmethods, including but not limited to pick-and-place or direct transfer.In step 210, connections are formed for the device 100 and the MISstructure 112. In addition, other optical layers and devices may beintegrated to the system substrate after the transfer process.

Another example of a process to form the MIS structure 112 on the microdevice 100 is illustrated in FIG. 2B. First the micro devices 100 areformed in step 200. During step 200, the micro devices 100 may be formedby patterning or by selective growth. During step 202, the micro devices100 are prepared for transfer, which may include cleaning or moving to atemporary substrate. During step 204-1, part of the MIS structure 112 isformed, for example by deposition and patterning a dielectric layer, onone surface of the micro device 100. During step 206, the micro devices100 are again prepared for transfer, which may include a lift-offprocess, cleaning process, and/or other steps. In addition, during step206, connection pads or electrodes for micro devices 100 or MISstructure 112 are deposited and/or patterned. During step 208, selectedmicro devices 100 may be transferred to a receiver substrate. Thetransfer may be done by various methods including but not limited topick-and-place or direct transfer. The MIS structure 112 may then becompleted during step 204-2, which may include deposition and patterningof a conductive layer. During step 210, connections are formed for themicro devices 100 and the MIS structure (or structures) 112. Otheroptical layers and devices may be integrated to the system substrateafter the transfer process. Step 210 may be the same as step 204-2 or adifferent and/or separated step. Other process steps may also beexecuted in between steps 204-2 and 210. In one example, a passivationor planarization layer may be deposited and/or patterned prior to step210 to avoid shorts between MIS electrodes and other connections.

With reference to FIG. 2C, another example of a process to form MISstructure 112 on the micro device 100 is illustrated. First the microdevices 100 are formed in step 200 by patterning or by selective growth.During step 202, the devices 100 are prepared for transfer, which mayinclude cleaning or moving to a temporary substrate. In addition, duringstep 202, connection pads or electrodes for the function of the microdevice 100 and/or for the MIS structure 112 may be deposited and/orpatterned. During step 208, selected micro devices 100 may betransferred to the receiver substrate by various methods, such as butnot limited to pick-and-place or direct transfer. The MIS structure 112is then formed during step 204, e.g. on the receiver substrate, afterthe final transfer, which may include deposition and patterning ofdielectric and conductive layers. During the following step 210,connections are formed for the micro devices 100 and the MIS structures112. In addition, other optical layers and devices may be integrated tothe system substrate after the transfer process. Step 210 may share someof the same process steps with step 204 or be a completely separatestep. In the latter case, other process steps may be done between 204and 210. In one example, a passivation or planarized layer may bedeposited and/or patterned prior to step 210 to avoid shorts between MISelectrodes and other connections.

After patterning the micro devices 100, depending on the patterningprocess, each micro device 100 may have straight or sloped walls. Thefollowing descriptions are based on selected sloped embodiments, butsimilar or modified processing steps may be used for other embodimentsas well. In addition, depending on the transfer method, each microdevice face connected to the receiver substrate may vary and thereforeaffect the slope of the device wall. The processing steps described nextmay be used directly or modified to be used with other slopes and devicestructures.

FIG. 3 illustrates a plurality of micro devices 306, similar to microdevices 100, which have been transferred to a system or receiversubstrate 300. The micro devices 306 include a sidewall of faces with anegative slope i.e. at an acute angle with a top of the micro device 306and an obtuse angle with the bottom of the micro device 306 or with thesystem substrate 300. Each micro device 306 is connected to a circuitlayer 302 through at least one contact pad 304. Depending on the slopeof the sidewalls, an MIS structure may be formed using normal or polymerdeposition. The methods described herein may be used with somemodifications or directly for this case. However, if the slope is toosteep, the preferred way is to prepare the MIS structure on the microdevices 306 prior to transfer. An exemplary method for creating an MISstructure prior to transfer will be described hereinafter.

FIG. 4 illustrates a process flowchart for a basic wafer etching process1000 for forming a mesa structure formation. In step 1001, the wafersmay be cleaned, e.g. using piranha etching containing sulfuric acid andhydrogen peroxide, followed by cleaning with hydrochloric diluted DIwater. Step 1002 may include deposition of a dielectric layer. In step1006, the dielectric layer may be etched to create an opening on thelayer for subsequent wafer etching. In step 1008, the wafer substratemay be etched using a dry etching technique and chlorine chemistry todevelop mesa structures. In step 1010, hard mask may be removed by a wetor dry etching method, and the wafer may then be subsequently cleaned instep 1012.

Embodiments of a method to form an MIS structure in accordance withprocess 1000 are illustrated with reference to FIGS. 5A to 5D. The microdevices 406 may include a vertical sidewall structure, a negative slopesidewall structure or a positive slope sidewall structure (i.e., thesidewalls are at an acute angle with the base of the micro device 406and the system substrate 400). In FIG. 5A, each of the micro devices 406are transferred to a system substrate 400, and connected to a circuitlayer 402, which is formed or mounted on the system substrate 400,through at least one connection pad 404. After this step, the MISstructure may be initiated and completed or simply completed. Whiletraditional lithography, deposition, and patterning processes areapplicable to create or complete such structures and to connect themicro devices to proper bias connections, different methods may be usedwith further tolerance to misplacement of the micro devices.Specifically, in large area processes, micro device placement inaccuracymay be a few micrometers.

With reference to FIG. 5B, in this embodiment a dielectric layer 408 maybe deposited around the micro devices 406 to cover unwanted exposedportions of the contact pads 404. Openings for vias 418 may be formed(e.g., etched) in the dielectric layer 408 to connect a conductive layer412 of the MIS structure to the circuit layer 402. A similar ordifferent dielectric layer 410 may be deposited on at least one side ofeach of the micro devices 406, as part (i.e., the insulator part) of theMIS structure. The dielectric layer 410 deposition step may be conductedprior to transferring the micro device 406 to the system substrate 400,at the same time as the dielectric layer 408, or after deposition oflayer 408. Subsequently, the conductive layer 412 may be deposited andpatterned around and between each micro device 406, to complete the MISstructure. In an embodiment, the conductive layer 414 may connect atleast two micro device/MIS structures together. In addition, oralternatively, the conductive layer 416 may connect the MIS structure toa contact pad 404 of the micro device 406. The conductive layer 412 maybe transparent to enable other optical structures to be integrated intothe system substrate 400. Alternatively, the conductive layer 412 may bereflective to assist with light extraction, direction, reflection, orabsorption. The conductive layer 412 may also be opaque for someapplications. Further processing steps may be carried out after formingthe MIS structure, such as but not limited to depositing a commonelectrode or integrating optical structure/devices.

FIGS. 5C and 5D illustrate an exemplary structure for depositing acommon electrode 426 on an opposite side of the MIS structure to thesystem substrate 400. The upper surface of the MIS structure isplanarized (e.g., using a dielectric material) similar to dielectriclayer 408, and then patterned (e.g. etched) to provide access points toconnect the common electrode 426 to the micro devices 406. The commonelectrode 426 may be coupled to either the micro device 406, the MISstructure (i.e., conductive layer 412), or the circuit layer 402 throughpatterning (e.g., openings 420, 422, and 424).

The common electrode 426 may be transparent to the light from microdevices 406 to enable the light to pass therethrough, reflective to thelight from the micro devices 406 to reflect the light back through thesystem substrate 400, or opaque to the light from the micro devices 406to minimize reflection. The common electrode 426 may also be patternedto create addressable lines. Several other methods may be used fordeposition of the common electrode 426. Other optical devices andstructures may be integrated onto the system substrate or into thecircuit layer before or after the common electrode 426.

With reference to FIGS. 6A to 6C, an alternative process includesforming part or most of the MIS structure on a donor (or intermediate ororiginal) substrate 560 prior to transferring micro devices 504 to asystem substrate 500. The initial process steps may be conducted on theoriginal substrate used for micro devices 504 fabrication or on anyintermediate substrate. With reference to FIG. 6A, a first dielectriclayer 516 may be deposited prior to forming the MIS structure, which mayavoid any unwanted short/coupling between the MIS layer and the othercontacts after transfer. The MIS structure is formed by a gateconductive layer 512 and a dielectric layer 510 deposited around andbetween the micro devices 504. The dielectric layer 510 may be similarto first dielectric layer 516 or different. The first dielectric layer510 may also be a stack of different dielectric material layers. Inexample MIS structures 550 and 552, no top dielectric layer 518 isdeposited on top of the conductive layer 512. In example MIS structure552, the gate conductive layer 512 is recessed down from the top edge ofthe micro device 504 to avoid any short with a top electrode. However,the gate conductive layer 512 may cover the top edge of the micro device504, if desired. In example MIS structure 554, the gate conductive layer512 may include a wing portion that extends outwardly from an angledportion parallel to the donor substrate 560 beyond a dielectric layer518 to create easier access to create connections after transfer to asystem substrate. In addition, the micro device 504 may be covered witha second dielectric layer 518 with openings to connect to the microdevice 504 and the extended electrode 512. Example MIS structure 556 mayuse the second dielectric 518 to cover only the top side of theconductive layer 512 and the micro device 504, except for an opening forthe top electrode to contact the micro device 504.

FIGS. 6B and 6C show the micro devices 504 with MIS structures afterthey were transferred to the system substrate 500. During the transferprocess, the micro devices 504 may be flipped so that the bottom surfaceconnected to the donor substrate 560 is also connected to the systemsubstrate 500. A connection pad 506 may be provided between each microdevice 504 and the system substrate 500 to couple the micro devices 504to the circuit layer 502. Different methods may be used including theone described above to create a connection for the MIS structure andother electrodes (e.g., a common electrode). In another embodiment, theexample MIS structures 550 and 552 include a top electrode 541 coveringboth the micro device 504 and the gate conductive layer 512 of the MISstructure. The top electrode 542 may be connected to the circuit layer502 with a via 532 extending through the dielectric layer 516 or theelectrode 541 may be connected at the edge of the system substrate 500through bonding. In example MIS structure 554, an extension 540 of theconductive layer 512 may be used to couple the MIS structure (i.e., theconductive layer 512) to the circuit layer 502. The first dielectriclayer 516 may be extended on the system substrate 500 to cover theconnection pads 506 between micro device 504 and the system substrate500 to avoid possible shorts between the MIS structure and otherconnections. A top electrode 542 may be provided, as in example MISstructures 554 and 556, which extends through an opening in the topdielectric layer 518 into contact with the micro device 504. Withregards to example MIS structure 556, the MIS structure (e.g. theconductive layer 512) may be shorted to the device contact pads 506 orthe MIS structure may be aligned properly to have its own contact on thesystem substrate 500. For both example MIS structures 554 and 556,different post-processing steps may be used, similar to other structuresdisclosed herein. One example may be a common electrode deposition withor without planarization, as in FIG. 5D. Another example may be lightconfinement structure or other optical structures.

FIGS. 7A and 7B illustrate an alternative process, in which part or mostof the MIS structure are formed on the donor (or intermediate ororiginal) substrate 560 prior to their transfer to the system substrate500. The process may be done on the original substrate used forfabrication of the device or on any intermediate substrate. FIG. 7Aillustrates several different example MIS structures 650, 652 and 654,which may be formed on micro devices 604. However, other structures maybe used as well. A dielectric layer 616 may be deposited prior toforming the MIS structures, which may avoid any unwanted short/couplingbetween the MIS structure and other contacts after transfer. The MISstructure includes a conductive layer 612, and a dielectric (i.e.,insulating) layer 610. The dielectric layer 610 may be similar to 516 ordifferent. The dielectric layer 610 may also be a stack of differentdielectric material layers. In addition, a connection pad 614 may beformed on each micro device 604 that extends through an opening in thedielectric layer 610. In example MIS structure 650 and 652, nodielectric may be deposited on top of the conductive layer 612. However,in example MIS structure 654 an additional layer of dielectric 618 maybe provided for planarization and extra insulation between the contactpad 614 and the conductive layer 612. In example MIS structure 652, theconductive layer 612 may be contiguous (i.e., the same) as the contactpad 614. The conductive layer 612 may be recessed from the edge of themicro device 604 or the conductive layer 612 may cover the edge of thedevice 604. In structure 654, the conductive layer 612 includes anextension that extends parallel to the system substrate 660 to createeasier access to create connections after transfer to system substrate660. In addition, the micro device 604 may be covered with a dielectriclayer 618 with openings for connection of the contact pad 614 to themicro device 604 and the extended electrode 612 to the system substrate660.

FIG. 7B shows the micro devices 604 with MIS structures after beingtransferred to the system substrate 600. A connection pad 614 may beprovided between each micro device 604 and the system substrate 600 tocouple each micro device 604 to the circuit layer 602. Different methodsmay be used, including the ones described above, to create connectionsbetween the MIS structures and other electrodes (e.g. a commonelectrode). Another method is illustrated in FIG. 7B, for MIS structure650 and 654, in which the negative slope of the micro device 604 is usedto create a connection between the MIS structures 650 and 654, and thesystem substrate 600 through an electrode 618 that extends from theconductive layer 612 parallel to the system substrate 600 along the topof the dielectric layer 621. A conductive metal via 620 may extendthrough a passivation or planarization (e.g., dielectric) layer 621,into contact with the circuit layer 602. The passivation orplanarization layer 621 may be deposited prior to the electrode 618deposition and patterning. The micro device 604 may be covered duringelectrode deposition or the conductive layer 612 may be removed from thetop of the micro device 604 by patterning and etching. Using thenegative slope of the micro device 604 and the conductive layer 612 toseparate the top electrode 622 of the micro device 604 and the MISelectrode 618, minimizes misalignment therebetween, which is crucial forhigh throughput placement of the micro devices 604. The negative slopeof the side face of the micro device 604 and the conductive layer 612forms an acute angle with the circuit layer 602 and the system substrate600. For all structures, different post-processing steps may be used,similar to other structures disclosed herein. One example may be acommon electrode deposition with or without planarization. Anotherexample may be light confinement, or reflective structure or anotheroptical structure.

The methods described herein may be used for different structures andthe methods are just examples and may be modified without affecting theoutcome. In one example, any one of the top and bottom electrodes 622and 614 and the conductive layers 612 may be either transparent,reflective, or opaque. Different processing steps may be added betweeneach step to improve the device or integrate a different structure intothe device without affecting the outcome of creating the MIS structure.

Vertical Devices with Conductivity Modulation Engineering

FIG. 8A illustrates a schematic of a vertical solid state micro device,similar to micro devices 406, 504, and 604, showing lateral currentcomponents flowing from a top electrode layer, which is capable ofdirecting current through the bulk of the micro device in a device layer701. The device layer 701 is formed on a device substrate 700 withcontact pads 703 (i.e., the top electrode) formed (e.g., etched) on thedevice layer 701. A voltage source 704 may be connected to the contactpads 703 and a common bottom electrode 702, mounted on the devicesubstrate 700, to generate current to power the micro devices. Thefunctionality of device layer 701 is predominantly defined by thevertical current. However, due to the top surface lateral conduction ofthe device layer 701, current 705 with lateral components flows betweenthe contact pads 703 and the common electrode 702. In order to reduce oreliminate the lateral current flow 705, these techniques are suggested:

-   -   1. Top layer resistance engineering.    -   2. Full/partial etching modulation.    -   3. Material conductivity modulation.

In this way, the lateral current flow structure may be divided intothree main structures:

1) at least one conductive layer 703 with resistance engineering;2) a full or partial etching of one or more conductive layers 703, and3) a material for conductivity modulation (e.g., alternating conductiveand non-conductive sections or conductive sections separated bynon-conductive sections).

The conductive layer 703 with resistance engineering may be described asfollows. The semiconducting top layer of the device layer 701, justbefore the metallic contact 703, may be engineered to limit the lateralcurrent flow by manipulating the conductivity or thickness of theconductive layer 703. In one embodiment, when the top layer of thedevice layer 701 is a doped semiconducting layer, decreasing theconcentration of active dopants and/or the thickness of the layer maysignificantly limit the lateral current flows. Also, the contact areamay be defined to limit the lateral conduction. In another case, thethickness of the conductive layer 703 (or more than one conductivelayer) may be reduced. After that, the contact layer 703 may bedeposited and patterned. Deposition of the contact layer 703 may occuron an array of interconnected or contiguous micro devices or onnon-isolated micro devices. As a result, the active layers of the devicelayer 701 are not etched or separated to create individual microdevices. Therefore, no defect is created at the perimeter of theisolated micro devices, since the isolation is developed electrically bycontrolling the current flow.

Similar techniques may be used on isolated micro devices to diverge thecurrent from the perimeter of each micro device. In another embodiment,after the micro device is transferred to another substrate, the otherconductive layer(s) are exposed. The thickness of the device layer 701may be chosen to be high to improve device fabrication. After thecontact layer 703 is exposed, the thickness may be reduced, or thedopant density decreased, however, some of the contact layers 703 mayalso have a blocking role for the opposite charge. As a result, removingsome of the conductive layers of the contact layer 703 to thin the totalcontact layer resistance may reduce the device performance. However,conductive layer removal may be very efficient for single layerengineering.

With reference to FIG. 8B, another embodiment of a micro devicestructure in accordance with the present invention includes a partiallyetched top layer 716 of a micro device layer 718. In this embodiment,the top conductive layer 716 may be a p- or-n-doped layer in a diode.The material for conductivity modulation directs current through thebulk of the vertical solid state device in the device layer 718. Atleast one of the conductive layers (e.g., top conductive layer 716) inthe device layer 718 may be partially or fully etched, to formalternating raised conductive layer sections and open non-conductiveareas. The top conductive layer 716 below top contact 712 and on top ofthe device layer 718 may be fully or partially etched to eliminate orlimit the lateral current flow in the micro devices 714 formed in thedevice layer 718. Each micro device 714 is defined by the size of thetop contact pad 712. This is especially beneficial for micro devices 714in which the resistance manipulation of the top layer 716 will adverselyaffect the device performance. The thickness of the top conductive layer716 between adjacent devices 714 is reduced to make a higher resistancefor the current to flow in the lateral direction. An etching process maybe done using, for example, dry etching, wet etching or laser ablation.In many cases, the top contact 712 may be metallic and/or used as themask for the etching step. With full etching, the etching may stop at afunction layer of the device layer 718. In one embodiment, the topcontact 712 may be deposited on top of the conductive layer 716, and maybe used as the mask for etching the conductive layer(s) 716, potentiallyenabling fewer processing steps and a self-aligned structure. This isespecially beneficial for micro devices 714 in which the resistancemanipulation of the conductive layer 716 will adversely affect thevertical device performance. In this embodiment, the thickness of theconductive layer 716 is reduced in selected areas to make a higherresistance for the current to flow in the lateral direction. After thebottom conductive layers of the device layer 718 are exposed either bytransfer mechanism or etching substrate 710, the same etching processmay be performed. Again, the contact 712 may be used as the mask foretching the device layers 716 and 718.

With reference to FIG. 8C, another embodiment of a micro devicestructure in accordance with the present invention includes a topconductive modulation layer 722 on the device layer 718. As shown, theresistance of a (non-conductive or reduced-conductive) modulation area720 of the top conductive modulation layer 722 between adjacent contactpads 712 is manipulated (e.g., increased to greater than conductivelayer 722) to limit the lateral current flow components. Counter doping,ion implantation, and laser ablation modulation are examples ofprocesses that may be used to form the modulation areas 720 in thisembodiment. The ion implantation or counter doping may extend beyond theconductive layer 722 into the device layer 718 to further enhance theisolation between the current flowing through adjacent micro devices714. Similar to the full/partial modulation scheme, in this embodimentthe top contact 712 may be deposited on the top conductive layer 722first, and then used as a mask for the doping/implantation of the areas720. In another embodiment, oxidation may be used to form the modulationareas 720. In one method, a photoresist is patterned to match themodulation area 720, and then the devices are exposed to oxygen oranother chemical oxidant to oxidize the modulation areas 720. Then, thetop contacts 712 may be deposited and patterned. In another method, thetop contacts 712 are deposited and patterned first, and then the topcontact 712 is used as a mask for oxidation of the modulation areas 720.The oxidation step may be done on isolated devices or non-isolateddevices. In another embodiment, prior to oxidation, the total thicknessof the conductive layer(s) 722 may be reduced. The reduction step may bedone on selected modulation areas 720 for oxidation only. In anothercase, the oxidation may be done on the walls of the micro devices 714,which is especially applicable for isolated devices. Also, the bottomlayer of the device layer 718 may be modulated similarly after beingexposed. In another embodiment, the material conductivity modulation maybe done through electrical biasing. The bias for the areas 720 thatrequire high resistance is modified. In one embodiment, the effect onthe areas 720 may be extended to the device layers 718. Here, theconductive layer 722 may be modified (e.g., etched or implanted) withother methods described herein as well. In one embodiment, charge may beimplanted underneath area 720 inside device layers 718. The implantationmay be partial or all the way to the other side of the device layer 718.

In one embodiment, the bias modulation may be provided using an MISstructure, and the metal layer may be replaced with any other conductivematerial. For example, to prevent the current from the contact 712 fromgoing further away from the contact laterally, an MIS structure isformed around the contact 712. The MIS structure may be formed before orafter the contact is in place. In all above-mentioned embodiments, thearea of the active micro device 714 is defined by the top contact pads712 formed on the device layer 718.

The definition of the active device area by the top contact pad 712 maybe more readily applied to micro devices 714 with pillar structures.FIG. 8D illustrates a cross section of an MIS structure surrounding asingle contact layer 712; however, it is understood that the same may bedone for more than one contact layer 712. The device layer 718 is amonolithic layer comprising or consisting of pillar structures 722.Since the pillar structures 722 are not connected laterally, no lateralcurrent component exists in the device layer 718. One example of thesedevices is nanowire LEDs, in which each LED device consists of severalnanowire LED structures fabricated on a common substrate 710. In thiscase, as shown in FIG. 8D, the top metallic contact 712 defines theactive area of the LED structure 714. Device layers 718 with no lateralconduction are not limited to pillar structures and may be extended todevice layers 718 with separated active regions, such as layers withembedded nano or microspheres, or other forms.

In FIG. 8E, another embodiment of a micro device structure in accordancewith the present invention includes an MIS structure 715 surrounding thecontact layer 712. The MIS structure 715 comprises a top conductivelayer 716, a middle insulator (e.g., dielectric) layer 717, and a bottomsemiconductor layer 723, which may be a top layer of the device layer718. Biasing the conductive layer 716 of the MIS structure 715 to an offvoltage causes limited or no current to pass through the MIS structure715 laterally. The MIS structure 715 may be formed on the device layer718 or may be part of the transferred substrate, and the MIS structure715 defines the direction of lateral conduction. Other configurationsare conceivable, such as the conductive layer 716 may extend to bothsides of MIS structure 715, such that the dielectric 717 may extend overother conductive layers 712. The MIS structure 715 may be an open orclosed structure, or alternatively, a continuous or one-piece structure.In another embodiment, the dielectric 717 may comprise the oxidationlayers from a photoresist or masking step. Another dielectric layer maybe deposited on top of the oxidation layer, or a deposited dielectriclayer may be used by itself. In another embodiment, the conductivelayer(s) 716 may be removed so that the dielectric layer 717 is incontact with a semiconductor layer 723. The MIS structure 715 may alsobe formed on the walls of the micro device 714 to further deter currentfrom travelling to the edge of the micro device 714. The micro devicesurface may also be covered by a dielectric layer. For example, a gateconductive layer may be deposited and patterned for a gate electrode716, and then a dielectric layer 717 may be patterned using the gateelectrode 716 as a mask. In another method, the dielectric layer 717,which is an insulator, is patterned first, and then the gate electrode716 is deposited after. The gate electrode 716 and the contact 712 maybe patterned at the same time or separately. A similar MIS structure mayalso be made on the other side of the device layer 718 after it isexposed. The thickness of conductive layers 716 of the micro device 714may be reduced to improve the effectiveness of the MIS structure 715.Where selective etching or modulation of the conductive layer 716 oneither side of the vertical micro device 714 is difficult, the MISstructure method may be more practical, in particular if etching orresistance modulation may damage the active device layer 718. In thedescribed vertical structures, the active device area 714 is defined bythe top contact area 712. Here, the ion implantation in the dielectriclayer 717 or the charge storage in a floating gate 716 may be used topermanently bias the MIS structure 715.

FIGS. 8F and 8G illustrate a structure highlighting the use of adielectric layer 712-1 between the contact pads 712. The contact pads712 define the micro devices in a device layer 701 on top of a substrate700, which may be sapphire or any other type of substrate. The microdevices include a conductive layer 702 and a contact pad 712. In FIG.8F, the conductive layer 702 is intact, but in FIG. 8G the conductivelayer 702 is either etched, modified, or doped between each contact pad712 with a different carrier or ions. Some extra bonding layers 712-2may be placed on top of the contact pads 712, or the contact pads 712may comprise the bonding layers 712-2. The bonding layers 712-2 may befor eutectic bonding, thermocompression, or anisotropic conductiveadhesive/film (ACA/ACF) bonding. During the bonding, the dielectriclayer 712-1 may prevent the contact pads 712 from expanding to otherareas and creating contacts. In addition, the dielectric layer 712-1 mayalso be a reflector or a black matrix to confine the light further. Thisembodiment is applicable to the embodiments demonstrated in FIG. 8-11and all other related embodiments. The methods described here can beapplied to either side of the micro devices.

Method for Manufacturing LED Displays

Methods for manufacturing LED displays are described using LED devicesgrown on a common (e.g., sapphire) substrate. Each LED may comprise asubstrate 750, a first doped conductive layer 752 (e.g., n-type layer)active layers 754, and a second doped conductive layer 756 (e.g., p-typelayer) formed on the substrate 750. The following is described withreference to a Gallium Nitride-based (GaN) LED; however, the presentlydescribed vertical device structure may be used for any type of LEDswith different material systems.

With reference to FIG. 9A, the GaN LEDs are fabricated by depositing astack of material on the sapphire substrate 750. The GaN LED deviceincludes the substrate 750, such as sapphire, an n-type GaN layer 752formed on the substrate 750 or a buffer layer (for example GaN), anactive layer 754, such as a multiple quantum well (MQW) layer, and ap-type GaN layer 756. A transparent conductive layer 758, such as Ni/Auor ITO, is usually formed on the p-doped GaN layer 756 for betterlateral current conduction. Conventionally, a p-type electrode 760, suchas Pd/Au, Pt, or Ni/Au is then formed on the transparent conductivelayer 758. Since the substrate 750 (sapphire) is an insulator, then-type GaN layer 752 is exposed to make an n-contact 762 to the n-typelayer 752. This step is usually done using a dry etch process thatexposes the n-type GaN layer 752, and then deposits the appropriatemetal contacts for the n-contact 762. In LED display applications wheredisplay pixels are single device LEDs, each LED is bonded to a drivingcircuit which controls the current flowing into the LED device. Here,the driving circuit may be a thin film transistor (TFT) backplaneconventionally used in LCD or organic light-emitting diode (OLED)display panels. Due to the typical pixel sizes (10-50 μm), the bondingmay be performed at a wafer level scale. In this scheme, an LED wafer,comprised of isolated individual LED devices, may be aligned and bondedto a back-plane which is compatible with the LED wafer in terms of pixelsizes and pixel pitches. Here, the LED wafer substrate may be removedusing various processes such as laser lift-off or etching.

FIG. 9B illustrates a fabrication process of an LED display, includingthe integration process of a device substrate 801 with micro devices ina device layer 805 defined by top contacts 802, and bonding of thedevice substrate 801 to a system substrate 803. Micro devices aredefined using the top contact 802 formed on top of the device layer 805,which may be bonded and transferred to the system substrate 803 withcorresponding and aligned contact pads 804. For example, the microdevices may be micro LEDs with sizes defined by the area of their topcontact 802 using any methods explained above. The system substrate 803may be a backplane with transistor circuitry to drive individual microLEDs. In this process, the LED devices are isolated by dry etching andpassivation layers. Fully isolating the devices may create defects inthe active or functional layers, reducing the efficiency and imposingnon-uniformities. Since the perimeter compared to the area of the microdevices is more substantial as the device becomes smaller, the effect ofdefects become more noticeable. In one embodiment, a monolithic LEDdevice is converted into individual micro LEDs without etching theactive area and using lateral conductive manipulation. As a result,there is no sidewall within the micro LED to create defects. Thesurrounding walls across the array of LEDs may be thereby extended untilthey have no effect on the peripheral LED devices. Alternatively, a setof dummy LED devices around the array may be used to reduce the effectof the peripheral walls on the active micro LED devices. This techniquemay also be used to prevent or reduce the current going through thesidewalls.

In another embodiment, illustrated in FIG. 9C, an LED wafer may befabricated such that the device layer 805 includes a first dopedconductive (e.g., an n-type) layer 852 on a substrate 801 with thesecond doped conductive layer (e.g., a p-type) layer 854 as the toplayer, and the monolithic active layer 856 therebetween. Each contact802 defines an illumination area 860. The thickness of the second dopedconductive (e.g., p-type) layer 854 and conductivity may be manipulatedto control the lateral conduction through the device. This may be doneby either etching the pre-deposited conductive layer 854 or bydepositing a thinner second (e.g., p-type) conductive layer 854 duringthe LED structure fabrication. For the etching method, accuratethickness control may be achieved using a dry etching process. Inaddition, the material structure of the second (e.g., p-type) layer 854may be modified based on layer doping level to increase the layer'slateral resistance. The second doped conductive layer 854 does not haveto be limited to the p-type layer and may be extended to other toplayers in the LED structure. As a result of this modification, theillumination area 860 may be defined solely by the area of the depositedcontact layer 802 on top of the p-type film 854.

In another embodiment illustrated in FIG. 9D, to further limit thelateral illumination, the second doped conductive layer (e.g., p-layer)854 between two adjacent pixels may be fully or partially etched. Thisprocess step may be done after the contact layer (e.g., contacts 802) isdeposited in a process such as dry etching. In this case, the contactlayer 802 may be used as a mask for etching the second conductive layer854. Preferably the present structure limits or eliminates the wallpassivation of pixels, which results in a higher number of pixels in aspecific area of the wafer or higher pixels per inch (PPI). This mayalso be translated to fewer process steps and a lower fabrication costcompared to fully isolated LEDs with wall passivation.

In another embodiment illustrated in FIG. 9E, an LED wafer structure isdefined by the top contacts 802 and a sub-divided second dopedconductive (e.g., p-type) layer 854 including individual sectionsdefined by laser etching for example. Here, the second conductive layer854 (e.g., p-type) may be partially or fully removed using laserablation etching of the top conductive material (e.g., GaN). In thiscase, laser fluence defines the ablation rate, and any thickness of thesecond conductive (e.g., p-type GaN) layer 854 may be etched precisely.One example of such a laser is a femtosecond laser at red or infraredwavelengths. Here, the top metal contacts 802 or other protective layersare used as a mask in the laser etching process steps. Alternatively,the laser beam size may be defined using special optics to match thedesired etching region dimensions. In another example, shadow masks maybe used to define the sections of the second conductive layer 854 (i.e.,the etching regions) between contacts 802. Laser ablation etching mayalso be extended to the other layers (e.g., at least one of the activelayer 856 and the first conductive layer, such as n-type, layer 852, ofthe LED structure). In this case, the individual LED devices may beisolated fully or partially from each other. In this scenario, it may berequired to passivate LED etched walls by depositing dielectric layers.

In the above-mentioned embodiments, contacts 865 for the firstconductive layer 852 (e.g., n-layer contacts) may be formed after thefirst conductive layer 852 is exposed either by bonding and removing theLED wafer substrate 801 that connects to the backplane circuitry 803 orany other substrate, or by etching the substrate 801. In thisembodiment, the first (e.g., n-type) layer contact 865 may be atransparent conductive layer to enable light illumination therethrough.In this embodiment, the first (e.g., n-type) layer contact 865 may becommon for all or part of the bonded LEDs, as shown in FIG. 9F, whichillustrates an LED wafer, as herein described with particular referenceto FIGS. 9C to 9E, with the substrate 801 removed and replaced with acommon transparent n-contact 865, and the contacts 802 bonded to bondingpads 804 of the backplane structure 803. In cases where the LED devicestructure is grown on a semiconductor buffer layer, for example anundoped GaN substrate, in place of substrate 801, this buffer layer maybe removed after the LED transfer process to access the firstconductive, (e.g., n-type) layer 852. In the embodiment shown in FIG.9F, the entire GaN buffer layer is removed using processes such asdry/wet etching. As demonstrated in FIG. 9G in another embodiment, thefirst conductive (e.g., n-type) layer 852 may be connected to the commonelectrode 865 with a layer of alternating dielectric sections 871 anddoped conductive sections (e.g., n-type) 872, with the conductivesections 872 superposed over a corresponding contact 802 to define theillumination areas. The second conductive (e.g., p-type) layer 854 maybe connected to the contacts 802. In another embodiment, both the first(e.g., n-type) and the second (e.g., p-type) layers 852 and 854 may beconnected to a controlling electrode (e.g., 865) or a backplane (e.g.,803) for further pixelation.

FIG. 10A illustrates an integrated device 900 with micro devices definedby top contacts 903 bonded to a system substrate 904, which may includebonding pads 905. A common electrode 906, may be formed on top of thestructure. After transferring and bonding the device layer 902, whichcomprises a first conductive (e.g., n-type) layer, a second conductive(e.g., p-type) layer, and an active layer therebetween, a common topelectrode 906 may be deposited on the structure. For some optical devicelayers, the common top electrode 906 may be a transparent or areflective conductive layer. The second conductive (e.g., p-type) layermay be thinned to reduce the light scattering effect before depositingthe top contacts 903. In addition, a bank structure that has alternatingfirst conductive material, n-type, and dielectric sections, may be usedto define the pixels where the wall of the banks (i.e., dielectriclayer) are opaque or reflective layers, as described with reference toFIG. 9G.

With reference to FIG. 10B in an alternative embodiment, the LED wafer900 includes a buffer (e.g. dielectric) layer 908 and one or more commonmetallic contacts 910 (e.g., n-contact vias) extending through thebuffer layer 908 into contact with the device layer 902 (e.g., firstconductive, such as n-type). The integrated device 900′ includes microdevices defined by top contacts 903 bonded to a system substrate 904,ideally using contact pads 905. The common electrodes 910 may be formedat the edges of the device layer 902 and through the buffer layer 908 ontop of the device layer structure 902. As shown, the buffer layer 908 ispatterned around the edge to extend vias through the buffer layer 908 tomake metallic contacts to the first conductive (e.g., n-type) layer. Thetop layer of the integrated device layer structure 902 may be a layerwith low conductivity. For example, the top layer may be a buffer layerused during the growth of the device layer 902. In this case, the commonelectrodes 910 may be formed by making vias through the buffer layer908, for example at the edge of the structure to avoid the top bufferlayer.

With reference to FIG. 10C, a transferred LED wafer 900″ includes adevice layer 902 with a patterned first conductive (e.g., n-type) layer.Underneath the n-type layer is an active layer and a p-type layer, ashereinbefore described. To further decrease the lateral lightpropagation or adjust the device definition, the first conductive (e.g.,n-type) layer is patterned by partially or fully removing the firstconductive layer to form open channel grooves 907 between firstconductive sections, using the same structure as the front metalliccontact 910. Alternatively, the thickness of the first conductive layermay be reduced. The first (e.g., n-type) contact may be formed bydepositing a transparent conductive layer on top of the device layerstructure 902. The integrated device 900″ with micro devices defined bythe top contacts 903 may be bonded to a system substrate 904. The top ofthe device layer structure 902 is patterned to isolate micro deviceselectrically. The other layers (e.g., active and second conductive) anddevice layer 902 may be patterned or modulated to further isolate microdevices electrically and/or optically.

FIGS. 10D and 10E illustrate another embodiment of a transferred LEDwafer with a patterned first conductive (e.g., n-type) layer of thedevice layer 902. In cases where the buffer layer 908 is present, boththe buffer layer 908 and the first conductive (e.g., n-type) layer arepatterned with open channel grooves 907 between superposed firstconductive and buffer layer sections. In one embodiment, the patternedgrooves 907 may be further processed and filled with a material thatimproves the light propagation through the patterned area. An example ofthis is surface roughening to suppress total internal reflection and areflective material that prevents vertical light propagation in thegrooves 907. The integrated device 900′″ comprises micro devices definedby top contacts 903 bonded to a system substrate 904 using bonding pads905. The top of the structure is patterned to isolate micro deviceselectrically and optically, and common contacts 910 are formed at theedge of the device layer structure 902. If the buffer layer 908 exists,the buffer layer 908 needs to be patterned or modulated as well toisolate micro devices. Similar to the embodiment shown in FIG. 10B, thecommon contacts 910 may be formed, for example, at the edge of theactive layer structure 902 through vias in the buffer layer 908. Inaddition, color conversion layers (or color filter layers) may bedeposited on top of the patterned buffer or conductive layers 908 and902 to create a color display. In one case, the color conversion layers(or color filter layers) may be separated by a bank structure that maybe reflective as well.

An integrated device 900″″, illustrated in FIG. 10F, includes microdevices defined by top contacts 903 bonded to a system substrate 904with optical elements 914 formed in the grooves 907 between adjacentmicro devices. As shown, the open channel grooves 907 may be filled by alayer or a stack of optical layers 914 to improve the performance ofisolated micro devices. For example, in optical micro devices, theoptical elements 914 may comprise some reflective material to betteroutcouple the light generated by the micro devices in a verticaldirection.

FIG. 10G illustrates another embodiment of a transferred LED wafer900′″″ including the device layer 902 comprising a first conductive(e.g., n-type) layer 921, a second conductive (e.g., p-type) layer 922,and a monolithic active layer 923 therebetween. The second conductivelayer 922 is electrically connected to the backplane 904 using thecontacts 903 and corresponding contact pads 905 on the backplane 904.The first conductive layer 921 and the buffer layer 908 are patterned toform open channel grooves 907 between raised first conductive layerportions. As hereinbefore described, the grooves 907 may include lightmanagement elements 914 (e.g., reflective material to direct lightvertically and prevent scattering between micro devices).

In LED display applications where display pixels are single device LEDs,each LED should be bonded to a driving circuit which controls thecurrent flowing into the LED devices. Here, the driving circuit may be aTFT (Thin Film Transistor) backplane 904 conventionally used in LCD orOLED display panels. Due to the typical pixel sizes (10-50 μm), thebonding may be performed at a wafer level scale. In an embodiment, anLED wafer comprises isolated individual LED devices aligned and bondedto the backplane 904, which is compatible with the LED wafer (e.g., 900′or 900″) in terms of pixel sizes and pixel pitches. Here, the LED wafersubstrate may be removed using various processes, such as laser lift-offor etching. In this embodiment, it is important to isolate the LEDdevices by dry etching and passivation layers.

In another embodiment, illustrated in FIG. 10H, the original LED waferis fabricated with the second conductive (e.g., n-type) layer 922 as thetop layer. After the second conductive layer 922 is bonded to thebackplane 904 using the contacts 903 and the contact pads 905, theoriginal substrate is removed to expose the first contact (e.g.,p-layer) 921. The thickness and conductivity of the first conductive(e.g., p-type) layer 921 is manipulated to control the lateralconduction. This may be done by either etching the deposited firstconductive (e.g., p-type) layer 921 or by depositing a thinner p-layerto form alternating second conductive layer sections 921 a anddielectric layer sections 925 during the LED device layer structure 902fabrication. For the etching scenario, an accurate thickness control maybe achieved using a dry etching process. In addition, the materialstructure of the first conductive (e.g., p-type) layer 921 may bemodified in terms of the layer doping level to form alternating high andlow doped second conductive layer sections 921 a to increase the layer'slateral resistance. The modifications to the top layer are not limitedto the first conductive (e.g., p-type) layer 921 and may be extended toother top layers in an LED device layer structure 902. As a result ofthis modification, the illumination area may be defined solely by thedeposited conductive layer area on top of the p-type film.

To further limit the lateral illumination, the second conductive (e.g.,n-type) layer 922 between two adjacent pixels may be fully or partiallyetched. This process step may be done after the conductive layerdeposition in a process such as dry etching, as in FIGS. 9D and 9E. Inthis case, the contacts 903 in the contact layer may be used as a mask.One important advantage of this scheme is eliminating the wallpassivation of pixels which results in a higher number of pixels in aspecific area of the wafer, or higher pixels-per-inch (PPI). This mayalso be translated to fewer process steps and a lower fabrication costcompared to fully isolated LEDs with wall passivation.

FIG. 10H also shows an exemplary embodiment to integrate a color filteror color conversion layers 930 (and/or other optical devices) on top ofthe top electrode 906. Here, individual color filter sections of thelayer 930 may be separated by a bank (dielectric or insulating material)structure 931. The bank structure 931 may be reflective or opaque toensure that the light remains in the light emitting areas above thecontacts 903. The bank structure 931 may extend the dielectric layer 925that is used to separate second conductive layer sections 921 a, asillustrated in FIG. 10I. In the embodiment of FIG. 10I, the top commonelectrode 906 includes recesses that extend upwardly adjacent to thecolor filter sections 930, to receive the bank/dielectric structures931/925 that extend through both the second conductive layer 921 and thecolor filter section layer 930.

Other layers may be deposited on top of the color conversion and/orcolor filter layers 930. The structures of FIGS. 10H and 10I may beapplied to other embodiments, for example any of FIGS. 9 and 10, inwhich any one or more of the n-type layer, the buffer layer, and thep-type layer are patterned, thinned, or modulated with materialmodification techniques. The color conversion layer 930 may be comprisedof one or more materials such as phosphors, and nano materials, such asquantum dots. The color conversion layer 930 may blanket or coverselected areas. For a blanket deposition, the bank structure 931 may beeliminated. If the conductivity of the underlying first conductive(e.g., n-type) layer 921 is sufficient that the top common electrode 906may be eliminated.

With reference to FIG. 10J, the bank structure 931 may be replaced withfirst conductive layer sections 921 a, which extend from the firstconductive (e.g., n-type) layer 921. The first conductive (e.g., n-type)layer 921 may act as a common electrode or a common electrode 906 mayalso be provided. There may be a dielectric layer that separates part ofthe common electrode layer 906 from the first conductive layer section921 a to create further pixel isolation. The color conversion layerand/or color filter layers 930 may be deposited on the first conductivelayer 921, although some other buffer layers may be used. The colorconversion/filter layers 930 may be conductive to enable the topelectrode 906 to power the device layer 923, or an additional conductivelayer 935 may be included adjacent to or along with the colorconversion/filter layers 930. The top electrode 906 may be deposited ontop of the color conversion/first conductive layer section 921 a layers,if the conductivity of the first conductive layer 921 with the contactstructure 902 is not sufficient. The top common contact 906 may betransparent to enable generated light to pass therethrough, reflectiveto reflect generated light back through the structure 902, or opaque toabsorb light and further enhance the pixel isolation.

In another embodiment, illustrated in FIG. 10K, the first conductivelayer 921 may be etched to create pillar sections to form a bank betweenthe color filter sections 930. The top and portions of the sidewalls ofthe pillar sections may be covered by the top electrode 906, reflectivelayers, or opaque layers. The valleys in the first conductive layer 921may be filled with the color conversion and/or color filter layers 930.An additional conductive layer 935 (e.g., transparent) may be depositedonly at the bottom of the valleys or all over the area including thesidewalls to define the light emitting area. There may be a top commonelectrode 906 or other layer deposited over the entire structure 902,with raised sections that extend into the valleys into contact with theadditional conductive layer of the color filter layers 930. There may bea dielectric layer that separates part of the common electrode layer 906from the first conductive layer section 921 a to create further pixelisolation.

In another embodiment, illustrated in FIG. 10L, a second device layer902′ may be transferred and mounted on top of the first device layer902. The second device layer 902′ includes an additional firstconductive layer 921′, an additional second conductive layer 922′, andan additional active layer 923′. Additional contacts 903′ and 906′ arealso provided to supply power to the illumination areas. The stackeddevices 902 and 902′ may include a first planarization layer and/ordielectric layer 940 around the first device layer 902 and between thefirst and second devices 902 and 902′, as well as a second planarizationand/or dielectric layer 941 around the second device layer 902′. In oneembodiment, the surface of the first device layer 902 is planarizedfirst. Then, openings for electrical vias 945 may be opened (e.g.,etched) in the first planarization layer 940 to create contact with thebackplane 904. The contact (i.e., the vias) 945, may be at an edge or inthe middle of the first device layer 902. The second contact layer 903′,comprising traces and islands, are then deposited and patterned on topof the first planarization layer 940. Finally, the second device layer902′ is transferred on top of the second contact layer 903′. The processmay continue for transferring additional device layers 902. In anotherembodiment, the top contact 906 of the first device layer 902 may beshared with the bottom contact 903′ of the second device layer 902′. Inthis case, the planarization layer 940 between the first and seconddevice layers 902 and 902′ may be eliminated.

In another embodiment illustrated in FIGS. 11A and 11B, a device layer952, originally fabricated on a device substrate 950, is mounted on asystem substrate 958 using substrate contact pads or bumps 954, whichmay define the micro device illumination areas. The micro devices in theintegrated structure are partially defined by the contact bumps 954 onthe system substrate 958. In this embodiment, the device layer 952 maynot have any top contact to define the micro device area. The devicelayer 952 on the substrate 950 is bonded to a system substrate 958 withan array of contact pads or bumps 954 separated by an insulation (e.g.,dielectric) layer 956. The bonding may be made between the metalliccontact pads 954 and the device layer 952. This bonding process may beperformed using any bonding procedure, such as but not limited to heatand/or pressure bonding or laser heating bonding. An advantage of thisprocedure is eliminating the alignment process during the micro devicetransfer to the system substrate 958. The micro device size 960 andpitch 962 are partially defined by the size of the contact pad/bump 954.In one example, the device layer 952 may be LED layers on a sapphiresubstrate 950 and the system substrate 958 may be a display backplanewith circuitry required to drive individual micro LEDs that are definedpartially by the contact bumps on the backplane.

FIGS. 12A and 12B illustrate another integration process of a devicesubstrate 950 and a system substrate 958. The micro devices in theintegrated structure are fully defined by the contact bumps 954 on thesystem substrate 958. To precisely define the micro device size 960 andmicro device pitch 962, a bank layer 958 may be deposited and patterned(e.g., etched) onto the system substrate 958. The bank layer 958, whichmay include openings around each contact pad 954, may fully define themicro device size 960 and micro device pitch 962. In one embodiment, thebank layer 958 may be an adhesive material to fix the device layer 952to the insulation or dielectric layer 956 (i.e., to the system substrate958).

FIG. 12C shows the integrated device substrate 950 transferred andbonded to the system substrate 958, and FIG. 12D shows a common topelectrode 966 formed on top of the device layer structure 952. Afterbonding the micro device substrate 950 to the system substrate 958, themicro device substrate 950 may be removed using various methods, and thecommon contact 966 may be formed above the integrated structure 952. Foroptical micro devices, such as but not limited to micro LEDs, the commonelectrode 966 may be a transparent conductive layer or a reflectiveconductive layer. The bank structure 964 may be used to eliminate thepossibility of a short circuit between adjacent pads 954 after apossible spreading effect due to pressure on the pads 954 duringassembly. Other layers, such as color conversion layers, may bedeposited after the bonding process.

FIGS. 13A and 13B illustrate another embodiment of an integratedstructure in which a device layer 952 is mounted on a system substrate958 using one or a plurality of bonding elements 968 at the edge of thebackplane 958. In this embodiment, adhesive bonding elements 968 may beused at the edge of the backplane 958 to bond the device layer 952 tothe system substrate 958 or to the insulation layer 956 of the devicelayer 952. In one embodiment, the bonding elements 968 may be used totemporarily hold the device layer 952 to the system substrate 952 forthe bonding process of contact pads 954 to the device layer 952. Inanother embodiment, the bonding elements 968 permanently attach themicro device layer 952 to the system substrate 958.

FIGS. 14A to 14C illustrate another embodiment of an integration processof the device substrate 950 and the system substrate 958 with a postbonding patterning of the device layer 952 and the common electrode 966.In this embodiment, the device layer 952 may be patterned to includeraised contact sections (e.g., 1.5×-3.0× the thickness of the remainderof the conductive layer) over the contact pads 954, after beingtransferred to the system substrate 958. The patterning 970 may bedesigned and implemented to isolate micro devices electrically and/oroptically. After patterning the device layer 952, the common topelectrode 966 may be deposited on the device layer 952 formed around andon top of the raised contact sections. For optical devices, such asLEDs, the common electrode 966 may be a transparent conductive layer ora reflective conductive layer.

FIGS. 15A to 15C illustrate an alternative embodiment of an integrationprocess for the device substrate 950 and system substrate 958 with apost bonding patterning step, optical element, and common electrode 966formation. As illustrated, after transferring and patterning the devicelayer 952, similar to FIGS. 14A to 14C, additional layers 970 may bedeposited and/or formed between isolated micro devices to enhance theperformance of micro devices. In one example, the elements 970 maypassivate the sidewalls of the isolated micro devices to help tovertical out coupling of light in the case of optical micro devices,such as but not limited to micro LEDs.

In the embodiments illustrated in FIGS. 8 to 10 and all other relatedembodiments, a black matrix or reflective layer may be deposited betweenthe pads (703, 712, 954, 908) to increase the light output. A reflectivelayer or black matrix may be part of the electrode.

In the presently explained methods, a protective layer may be finallyformed on top of the integrated structure to act as a barrier andscratch resistance layer. Also, an opaque layer may be deposited afterthe micro device and patterned to form the pixel. This layer may sitanywhere in the stack. The opening allows light to pass through only thepixel array and reduces the interference.

The micro devices as described herein may be developed, for example, byetching a wafer and forming mesa structures. Mesa formation may be doneusing a dry or wet etching technique. Reactive ion etching (RIE),inductively coupled plasma (ICP)-RIE and chemical assisted ion beametching (CAIBE) may be employed for dry etching the wafer substrate.Chlorine-based gases such as Cl₂, BCl₃, or SiCl₄ may be used to etch thewafer. Carrier gases including but not limited to Ar, O₂, Ne, and N₂ maybe introduced into the reactor chamber to increase the degree ofanisotropic etching and sidewall passivation.

With reference to FIGS. 16A to 16C, a device structure 1100 includes adevice layer 1202 deposited on a wafer surface 1200. Following the wafercleaning step, a hard mask 1206 is formed on the device layer 1202. Inan embodiment, a dielectric layer 1204, such as SiO₂ or Si₃N₄, is formedon the device layer 1202 using appropriate deposition techniques, suchas plasma-enhanced chemical vapour deposition (PECVD). The hard maskphotoresist 1206 is then applied on the dielectric layer 1204. In thephotolithography step, a desired pattern is formed on the photoresistlayer 1206. For example, PMMA (Poly(methyl methacrylate)) may be formedon the dielectric layer 1202 followed by a direct e-beam lithographytechnique to form the openings in the PMMA 1206.

FIG. 16B illustrates the device structure 1100 with the dielectric layer1204 etched to create openings on the device layer 1202 for subsequentwafer etching. A dry etch method with fluorine chemistry may be employedto selectively etch the dielectric layer 1204. Carrier gases, includingbut not limited to N₂, Ar, or O₂, may be introduced to control thedegree of anisotropic etching. Gas flow rate and mixture ratio, type ofcarrier gases, RF and DC powers, as well as substrate temperature may beadjusted to achieve the desired etching rate and high degree ofanisotropy.

FIG. 16C illustrates mesa structures 1208 and 1210 after the waferdevice layer 1202 etching step. In one embodiment, mesa structures 1208with straight sidewalls (e.g., perpendicular to the upper surface of thesubstrate 1200) may be formed. In another embodiment, mesa structures1210 with sloped side walls (e.g., forming an acute angle with the uppersurface of the substrate 1200) may be formed. The gas mixture ratio,type of gases in the reactor, and relevant etching conditions may beadjusted in order to modify the slope of the sidewalls. Depending on thedesired mesa structure 1208 and 1210, a straight, positive, or negativeslope sidewall may be formed. In an embodiment, sidewall passivationduring the etching step may be used to create a desired sidewallprofile. In addition, a cleaning step may be used to remove thepassivation layer or the native oxide from the sidewall. Cleaning may bedone using acetone or isopropyl alcohol followed by surface treatmentusing (NH₄)₂ and/or NH₄OH.

In an embodiment, an MIS structure may be formed after the mesastructure formation of FIGS. 16A to 16C. With reference to FIGS. 17 and18A to 18D, a process flow 1000B to form an MIS structure includesprocess steps 1114 and 1116, in which dielectric and metal layers 1402and 1404 are deposited on mesa structures (e.g., 1208 and 1210) to formMIS structures. Following the deposition of the dielectric layer 1402,in process 1116, a metal film 1404 is deposited on the dielectric layer1402 using a variety of methods, such as thermal evaporation, e-beamdeposition, and sputtering (FIG. 18A). In process step 1118, a desiredpattern is formed on the wafer using a photolithography step. In step1120, the metal layer 1404 is etched using dry or wet etching to form anopening on the top side of the mesa structure above the dielectric layer1402 (FIG. 18B). In step 1122, a photolithography step may be used todefine the dielectric etch area. In another embodiment, the etched metallayer 1404 may be used as a mask to etch the dielectric layer 1402 (FIG.18C). In step 1126, a second dielectric layer 1406 may be deposited onthe metal interlayer 1404 (FIG. 18D). In step 1128, an ohmic (e.g.,p-type) contact 1408 may be deposited on the micro device mesastructures 1208 and 1210, as shown in FIG. 18E. In process step 1130, athick metal 1410 is deposited on the contact 1408 for subsequent bondingof the mesa structures 1208 and 1210 to a temporary substrate in waferlift-off process steps from the native substrate.

FIG. 18A shows the dielectric layer 1402 and the metal layer 1404deposited on the mesa structure to form an MIS structure. A variety ofdielectric layers 1402 may be used, which include but are not limited toSi₃N₄ and oxides such as SiO₂, HfO₂, Al₂O₃, SrTiO₃, Al-doped TiO₂,LaLuO₃, SrRuO₃, HfAlO, and HfTiO_(x). The thickness of the dielectriclayer 1402 may be a few nanometers or up to a micrometer. A variety ofmethods, such as CVD, PVD, or e-beam deposition, may be used to depositthe dielectric layer 1402. In an embodiment, a high-k oxide dielectriclayer 1402 may be deposited using an atomic layer deposition (ALD)method. ALD enables very thin and high-K dielectric layers to be formedon the wafer. During ALD deposition of the dielectric oxide layer,precursors are introduced in the reaction chamber sequentially to form athin insulator layer. Metal precursors for the metal layer 1404 includehalides, alkyls and alkoxides, and beta-diketonates. Oxygen gas may beprovided using water, ozone, or O₂. Depending on the process chemistry,dielectric film deposition may be done at room temperature or at anelevated temperature. Deposition of Al₂O₃ may also be done usingtrimethylaluminum (TMA) and water precursors. For HfO₂ ALD deposition,both HfCl₄ and H₂O precursors may be used. Metal electrodes 1410 serveas biasing contacts for electric field modulation in the device. Metalcontacts 1408 include but are not limited to Ti, Cr, Al, Ni, Au, or ametal stack layer.

FIG. 18B shows the wafer with a pattern formed using a photolithographystep. FIG. 18C illustrates the wafer with a dry-etched dielectric layer1402 dry-etched (e.g., using fluorine chemistry). An etch stop foretching the dielectric layer 1402 may be the top surface of the mesastructure 1208 and 1210. As illustrated in FIG. 18D, the seconddielectric layer 1406 may be deposited on the metal interlayer 1404 forsubsequent p-contact deposition in order to prevent shorting with thedevice functional electrodes 1408 and 1410. Subsequently, the seconddielectric layer 1406 on top of the mesa structure may be etched tocreate an opening on the top surface of the mesa structures.

With reference to FIG. 18E, the ohmic (e.g., p-type) contact 1408 maythen be deposited on the mesa structure to enable power from externalelectrical power sources to be input to the micro devices. The contact1408 may be deposited using thermal evaporation, sputtering, or e-beamevaporation. Au alloys such as Au/Zn/Au, AuBe, Ti/Pt/Au, Pd/Pt/Au/Pd,Zn/Pd/Pt/Au, or Pd/Zn/Pd/Au may also be used for the contact 1408. Thesubsequent patterning step removes metal from unwanted areas allowingthe contact 1408 to be formed only on the top surface of the mesastructures. A thick metal 1410 may be deposited on the contact 1408 tosubsequently bond the mesa structures to the temporary substrate duringthe wafer lift-off process steps from the native substrate.

The scope of this invention is not limited to LEDs. One can use thesemethods to define the active area of any vertical device. Differentmethods, such as laser lift-off (LLO), lapping, or wet/dry etching maybe used to transfer micro devices from one substrate to another. Microdevices may be first transferred to another substrate from a growthsubstrate and then transferred to the system substrate. The presentdevices are further not limited to any particular substrate. Mentionedmethods may be applied on either the n-type or p-type layer. For theexample LED structures above, n-type and p-type layer positions shouldnot limit the scope of the invention.

Although an MIS structure was disclosed in this document as the methodto manipulate the electric field in the micro device to manipulate thevertical current flow, one can implement other structures and methodsfor this purpose. In an embodiment, electric field modulation may bedone using a floating gate as a charge storage layer or conductivelayer. FIG. 19 shows an exemplary embodiment of a micro device 1500 witha floating gate structure. The structure comprises a floating gate 1514that may be charged with different methods to bias the MIS structure.One method is using a light source. Another method is using a controlgate 1512 that is isolated with a dielectric layer 1516 from thefloating gate 1514. The biasing control gate 1512 enables charges to bestored in the floating gate 1514. Stored charges in the floating gate1514 manipulate the electric field in the device. When the micro device1500 is biased through the functional electrodes 1502 and 1504, thecurrent flows vertically which results in the generation of light. Themanipulated electric field in the micro device 1500 limits lateralcurrent flow, resulting in enhanced light generation.

FIG. 20 illustrates a schematic structure of the micro device 1500 witha floating gate charge storage layer 1514. The illustrated micro device1500 includes angled sidewalls as an example, but the micro device 1500may include different (e.g., vertically, negatively, and positively)angled sidewall. First, a thin dielectric layer 1516 is formed on themicro device 1500. The thickness of dielectric layer 1516 may be between5 nm to 10 nm to enable quantum mechanical tunneling of charges throughthe dielectric layer 1516. Oxide or nitride based dielectric materialsmay be used to form the thin dielectric layer 1516, including but notlimited to HfO₂, Al₂O₃, SiO₂, and Si₃N₄. The floating gate 1514 may beformed on the thin dielectric layer 1516. The floating gate 1514 may beformed from thin polysilicon or a metal layer as a charge storage layer.In another embodiment, the floating gate 1514 may be replaced withdielectric material to form a charge trapping layer. The dielectric inthe floating gate 1514 may be the same as the thin dielectric 1516 or adifferent layer. The dielectric layer of the floating gate 1514 may becharged by different techniques such as implantation. The dielectricmaterials include but are not limited to HfO₂, Al₂O₃, HfAlO, Ta₂O₅,Y₂O₃, SiO₂, Tb₂O₃, SrTiO₃, and Si₃N₄ or a combination of differentdielectric materials to form a stack of layers that may be used for thecharge trapping layer. In another embodiment, semiconductor or metalnanocrystals, or graphene may be used as the charge trapping layer.Nanocrystals including but not limited to Au, Pt, W, Ag, Co, Ni, Al, Mo,Si, and Ge may be used for charging trap sites. The nanocrystals createisolated trap sites. This in turn reduces the chance of charge leakagedue to the presence of defects on the thin dielectric layer 1516. Inaddition, if charges leak from one nanocrystal, it will not affect theadjacent sites as they are isolated from each other. On top of thefloating gate or charge trapping layer 1514, a second, thick dielectriclayer 1518 isolates the floating gate 1514 in order to prevent chargeleakage. The second dielectric layer 1518 may be made of variousdielectric materials, including but not limited to HfO₂, Al₂O₃, HfAlO,Ta₂O₅, Y₂O₃, SiO₂, Tb₂O₃, or SrTiO₃ with a thickness of 10 nm to 90 nm.On top of the second dielectric layer 1518, a control gate 1512 isprovided, which is responsible for floating gate 1514 charging. Thecontrol gate 1512 may be comprised of one or more conductive layers,such as metal, transparent conductive oxides, or polymers.

With reference to FIG. 21, a process flow 2000 to develop a floatinggate structure on the sidewalls of a micro device 1500 includes a firststep 1600 to form the micro devices 1500 (e.g., as in any of the methodshereinbefore described). During step 1600, either the micro devices 1500are formed by patterning or by selective growth. During step 1602 thedevices 1500 are transferred to a temporary or system substrate. Duringstep 1604, the thin dielectric layer 1516 is formed on the micro device1500. In step 1606, the floating gate or charge trapping layer 1514 isformed on the thin dielectric layer 1516. During step 1608, the second,thick isolation dielectric layer 1518 is formed on the floating gate1514. In step 1610, the control gate 1512 is formed on the thickdielectric layer 1518. In step 1612, a protective layer is formed on thestructure. The order of these steps in these processes may be changedwithout affecting the final results. Also, each step may be acombination of a few smaller steps. For example, the structure may beformed before transferring the micro device 1500 from the donorsubstrate to the acceptor substrate. In another embodiment, parts of thefloating gate structure may be formed before the micro device transferprocess and the floating gate structure may be completed after thetransfer step. In another embodiment, the entire floating gate structuremay be formed after the micro device transfer step.

Accordingly, a process of forming a micro device with a floating gate orcharge trapping structure, comprises forming the micro devices includinga functional electrode; and forming a first dielectric layer or a changetrapping layer on the first sidewall of the micro device.

In addition, the process may include forming a floating gate layer or acharge trapping layer on the first dielectric layer.

In addition, the process may include forming a second dielectric layeron the floating gate or charge trapping layer.

In addition, the process may include forming a control gate on thesecond dielectric layer.

An alternative embodiment of this process, wherein the first dielectriclayer may be between 5 nm to 10 nm thick to enable quantum mechanicaltunneling of charges therethrough.

An alternative embodiment of the process, wherein the second dielectriclayer may be between 10 and 90 nm thick to isolate the floating gate inorder to prevent charge leakage.

An alternative embodiment of the process, wherein the floating gate maybe comprised of polysilicon or a metal layer as a charge storage layer.

An alternative embodiment of the process, wherein the charge trappinglayer comprises semiconductor nanocrystals, metal nanocrystals, orgraphene.

An alternative embodiment of the process, wherein the nanocrystals maybe selected from the group consisting of Au, Pt, W, Ag, Co, Ni, Al, Si,and Ge.

An alternative embodiment of the process, further comprising biasing thecontrol gate and the functional electrodes to generate an electric fieldto enable charges to be injected from a charge transport layer in themicro device into the floating gate through the thin dielectric layer.

An alternative embodiment of the process, wherein the charge injectioncomprises Fowler-Nordheim tunneling or a hot electron injectionmechanism.

An alternative embodiment of the process, wherein the charge injectionmay be conducted by photoexcitation of the charge transport layer.

An alternative embodiment of the process, wherein the charge injectioncomprises exposing the micro device to ultraviolet light resulting inhigh energetic charges that overcome a potential barrier between thecharge transport layer and the first dielectric layer.

An alternative embodiment of the process, wherein the floating gate orcharge trap layer comprises a combination of two different dielectriclayers.

In an alternate embodiment, a first electrode contact extends from abottom contact layer of the micro device on one side of the microdevice; a second electrode contact extends upwardly from a top contactlayer of the micro device; and a third electrode contact extendsupwardly from the floating gate on another side of the micro device.

In an alternate embodiment, the first and third electrode contactsextend upward from the same side of the micro device.

In an alternate embodiment, the first and third electrode contactsextend upwardly from an opposite side of the micro device.

In an alternate embodiment, the first and second electrode contactsextend outwardly from opposite top and bottom surfaces of the microdevice.

Accordingly, another process of forming a micro device with a floatinggate or charge trapping structure comprises:

forming the micro devices including a functional electrode; and

forming a first dielectric layer or a charge trapping layer on the firstsidewall of the micro device.

In addition, the process may include charging the first dielectriclayer.

The process may include forming a second dielectric layer on the chargedfirst dielectric layer.

An alternative embodiment of the process, wherein the step of chargingthe first dielectric layer comprises ion bombardment to create fixedunneutralized charges on a surface of the first dielectric layer.

An alternative embodiment of the process, wherein the ions are selectedfrom the group consisting of Ba, Sr, I, Br, and Cl.

An alternative embodiment of the process, further comprising implantingsemiconductor ions in the first semiconductor layer to form a chargetrap layer.

An alternative embodiment of the process, wherein the semiconductor ionsmay be selected from the group consisting of Si+ and Ge+.

An alternative embodiment of the process, further comprising annealingthe first dielectric layer to cure stress on the dielectric layer afterion bombardment, and also enable diffusion of ions into the firstdielectric layer.

Accordingly, another process of forming a micro device with enhancedsidewalls comprises forming the micro devices including a functionalelectrode; and creating an intrinsic charges interface at the sidewallsby depositing semiconductor layers on a first sidewall with a differentband diagram compared to the sidewalls.

Referring to FIG. 22, a floating gate or charge trapping layer 1714 maybe charged by employing a variety of methods. In one embodiment, acontrol gate 1706 and one of the functional electrodes 1702 or 1704 arebiased so that a generated electric field allows charges 1708 to beinjected from the highly doped charge transport layer in micro device1700 into the floating gate 1714 through the thin dielectric layer 1716.Charge injection may be Fowler-nordheim tunneling or a hot electroninjection mechanism. For hot electron injection, charge injection may bedone by applying high voltage bias so that energetic charges canovercome the potential barrier between the charge transport layer andthe thin dielectric layer 1716. In another embodiment, charge injectionmay be done by photoexcitation of the charge transport layer. In thiscase, the device 1700 may be exposed to ultraviolet light, resulting inhigh energetic charges that can overcome the potential barrier betweenthe charge transport layer and the thin dielectric layer 1714.

In another embodiment illustrated in FIG. 23, a floating gate or chargetrap layer 1810 formed on the first, thin dielectric layer 1816 may be acombination of two different dielectric layers. A biasing control gate1806, enables charging an intermediate dielectric layer 1808. Thecharged intermediate dielectric layer 1808 creates image chargesopposite to the floating gate or charge trap layer 1810. With thistechnique, the floating gate 1810 may be controlled to be positive ornegative to allow electric field propagation direction to inward oroutward from the micro device sidewall.

In another embodiment, illustrated in FIG. 24, an electric fieldmodulation structure may be formed without using a control gate. Adielectric layer 1908 is formed on the sidewall of a micro device 1900.The formed dielectric layer 1908 may be permanently charged by ionbombardment or implantation to form a charge layer 1906. The chargelayer 1906 may be at either side or in the middle of the dielectriclayer 1908. Dielectric materials including but not limited to HfO₂,Al₂O₃, HfAlO, Ta₂O₅, Y₂O₃, SiO₂, Tb₂O₃, SrTiO₃, and Si₃N₄ or acombination of different dielectric materials to form a stack of layersmay be used for charge trapping layer 1906. Ion bombardment createsfixed unneutralized charges in the charged layer 1906, hence creating anelectric field in the body of the semiconductor. The ions may bepositive or negative, such as barium and strontium, iodine, bromine, orchlorine. In addition, semiconductor ions such as Si+ and Ge+ may beimplanted to form a charge trap layer. Following the ion implantation,the dielectric layer 1906 may be annealed to cure stress on thedielectric layer 1906 after ion bombardment, and also enable diffusionof ions into the dielectric layer 1908. Following the ion implantationand subsequent annealing, a thick dielectric layer 1908 is formed as anisolation and protective layer. The fixed charges in the dielectriclayer 1908 manipulate the electric field at the semiconductor/dielectriclayer interface to pull away charges in the semiconductor from theinterface toward the middle of device 1900 to limit lateral currentflow. Here, the ion/charge implantation may be done directly in thedielectric layer 1908. A barrier layer may be used between thedielectric layer 1908 and the micro device 1900 to protect the microdevice 1900 from the high energy ion particles during the creation ofthe charging layer 1906.

With reference to FIGS. 25 and 26, in another embodiment related tobiasing an MIS structure 2016 on a micro device 2010, eithercontact/electrode 2012 or 2014 of a micro device 2010 may be extendedover the MIS gate (the gate may be an actual layer, such as a conductivelayer, or only a position in a dielectric or other material to hold thecharge) while a dielectric layer 2018 a separates the MIS biasing gateand the micro device electrode 2012.

With reference to FIG. 25A, the contacts 2012 and 2014 of the microdevice 2010 may extend upwardly. To create an MIS structure 2016 (i.e.including a gate, such as a conductive layer) and a dielectric layer,for such devices, an MIS contact/gate pad 2022 to the MIS gate alsoextends upwardly. This structure may simplify the process of integratingthe micro devices 2010 into a receiver substrate as similar bonding orcoupling processes may be used for both MIS contact 2022 and the microdevice contacts 2012 and 2014. To avoid a short circuit between themicro device 2010 layers and the MIS 2016 gate, a dielectric layer 2020a is deposited. The dielectric layer 2020 a may be part of the MISstructure or a separate dielectric layer deposited independently. Inaddition, to avoid shorts during the bonding and/or integration of themicro device 2010 into a system (i.e., receiver) substrate, one or moredielectric layers 2018 a and 2018 b may cover the MIS structure 2016. Tocreate the contact to the micro device 2010 for one of the electrodes2012 and 2014, the dielectric layer 2020 b may be removed or opened(e.g., etched). The dielectric layer 2020 b may be the same as any oneor more of dielectric layers 2018 b, 2020 a, and 2018 a, or a separatelayer altogether. The space between the contacts 2014, 2022, the MISstructure 2016 and the micro device 2010 may be filled with a differenttype of materials, such as polymer or dielectrics. The filler may be thesame as the dielectric layers 2018 a and 2018 b, or different. Theposition of the MIS contact/gate pad 2022 and the micro device contact2014 may be different relative to the micro device 2010 or positionedsymmetrically on either side thereof. In another embodiment, the MISstructure may be formed using a charged layer and therefore no MIScontact 2022 will be needed.

In another embodiment presented in FIG. 25B, the contacts 2012 and 2014on the microdevice 2010 electrodes are on the same surface. To create anMIS structure 2016 for such devices, one can put the contact 2022 to theMIS gate on the same surface as the micro device contacts. Thisstructure can simplify the process of integrating said micro devicesinto a

receiver substrate as similar bonding or coupling processes can be usedfor both the MIS contact and the micro device contacts. In thisstructure, the gate pad 2022 is deposited on top of the vertical devicestructure. Therefore, at least one of the MIS layers is extended abovethe top of the device to provide space for the pads. In addition, toavoid shorts during the bonding and/or integration of the micro deviceinto the system (i.e., receiver) substrate, a dielectric layer 2018 aand 2018 b covers the MIS structure. To create a contact 2014 to themicro device for one of the electrodes, the dielectric layer 2020 b canbe removed or opened. The dielectric layer 2020 b can be the same aseither dielectric layers 2018 a or 2018 b. The space between thecontacts 2014, 2022, and the MIS 2016 (or micro device 2010) can befilled with different types of materials such as polymer or dielectrics.This filler can be the same as the 2018 a and 2018 b dielectric layer.

In an embodiment presented in FIG. 25C, a micro device consists of amesa structure 2010, contacts 2012, 2014, and 2022, and the MISstructure 2016. The contacts 2012 and 2014 of the micro device 2010electrodes are on the same surface. This structure can simplify theprocess of integrating said micro devices into a receiver substrate assimilar bonding or coupling processes can be used for both the MIScontact and the micro device contacts. To avoid the short between themicro device 2010 layers and the MIS 2012 gate, a dielectric layer 2020a is deposited. The connection 2014-b to a mesa layer is extended by atrace 2014-a for the contact 2014 and the MIS structure 2016.

In another embodiment, shown in FIG. 25D, there is no MIS underneath thetrace transferring the contact 2012. Here, the trace 2014-a can bedeveloped by patterning the same layer as the metal (conductive) layerof the MIS 2016.

FIG. 25E shows another embodiment where the contact for MIS electrode2022 and one of the device contacts (or pads) 2012 is on the first sideof the device 2010 and at least one contact 2014 for the device is on aside different from the first side where device 2010 is located.

FIG. 25F shows another embodiment where the contact for MIS electrode2022 and one of the device contacts (or pads) 2012 is on the first sideof the device 2010 and at least one contact 2014 for the device is on aside different from the first side where device 2010 is located. Here,the MIS contact 2022 is on top of the vertical device.

It is possible for all embodiments that the MIS contact 2022 ispartially sitting on top of the device, on the side of the device, or onthe etched layers.

The dielectric layers in different embodiments can be stacks ofdifferent layers. In one case, a thin ALD layer can be used first andthen a PECVD deposited dielectric (e.g., SiN) layer can be used to getbetter coverage and avoid shorts at the edges and corners. Also, thebiasing can be created or developed through band engineering. Usingdifferent layers with different band structure can create an intrinsicpotential that can bias the edge (i.e., side walls or top and bottomsurface) of the micro devices. Also, other biasing and integrationmethods presented here for MIS structures can be used with said microdevice structure with contact to the electrode on the same surface.

The position of the MIS contact 2022 and the micro device contact 2014can be different relative to the micro device 2010.

FIG. 26A illustrates a top view of the micro device 2010 with the MIScontact 2022 and the micro device bottom contact 2014 located onopposite sides thereof.

FIG. 26B, the MIS contact 2022 and the micro device bottom contact 2014are located on the same side of the micro device 2010. In this case, thedielectric layers 2020 a and 2020 b may be the same layer 2020.

FIG. 26C, the MIS contact 2022 and the micro device bottom contact 2014are located on two neighboring sides of the micro device 2010. The microdevice 2010 may have other cross-sectional shapes, such as a circle, andthe aforementioned positions may be modified to accommodate the microdevice shape. The dielectrics 2018 and 2020 may be a stack of differentlayers, and the conductive (gate) layers may be metal, any otherconductive material, or a stack of different materials.

FIG. 26D shows an exemplary top view of a micro device 2010 with the MIScontact 2022, while the micro device contact 2014 is located on adifferent part of the device. Here, the conductive layer 2016-a and thedielectric layer 2016-b form the MIS structure. Here, the dielectriclayer 2018 covers at least where the trace 2014-a passes. The MISstructure can be underneath trace 2014-a or outside of that area. Ifthere is no MIS underneath the trace 2014, the dielectric layer 2018 canbe the same as the MIS dielectric layer 2016-b. In this case, the trace2014 can also be the same as the conductive layer 2016-a of the MISstructure.

FIG. 26E shows another embodiment where the contact for the MISelectrode 2022 and the devices 2014 and 2012 are in one direction.

The following embodiments, illustrated in FIGS. 27 to 30, include arraysof optoelectronic devices, in which the pixelation may be developed bycreating pillars of the ohmic contact layer(s)/conductive layer andbonding an array of separated pads to the ohmic contact layer/conductivelayer. The pillars may be smaller than the pads. Some of thesemiconductor layers after the ohmic layer may be patterned. In someembodiments, the patterning of the semiconductor layers follows the samepattern as the pillars of the ohmic layer.

With reference to FIG. 27A, different conductive and active layers 2022are deposited on top of a device substrate 2020, followed by otherconductive or blocking layers 2024. The first conductive layer 2024 maybe p-type, n-type, or intrinsic. To create pixelated devices, theconductivity of the first conductive layer(s) 2024 may modulate intopillars of higher performance electrical connectivity. The pillars maybe smaller (e.g., ½ to 1/10 the pixel size, such as pad 2032 or smaller)whereby at least 1 to 10, preferably 2 to 8, and more preferably morethan 4, pillars contact each contact pad 2032. In one embodiment, thepillars are between 1 nm to 100 nm cubes. In one approach, the firstconductive layer(s) 2024 or part of the first conductive layer(s) may bepatterned (e.g., through lithography, stamping, and other methods). Inanother embodiment, a very thin pillar layer 2026 is deposited on thefirst conductive layer 2024, and then ideally annealed. The annealingprocess may be thermal or optical or a combination thereof. Theannealing may be done in ambient condition, vacuum, or with a differentgas. In one embodiment, the pillar layer 2026 may comprise ITO, gold,silver, ZnO, Ni, or other materials. The pillar layer 2026 may bedeposited by various means, such as e-beam, thermal, or sputtering.After creating the pillars 2026-i, a pad substrate 2030, which includespads 2032, and may include driving circuitry, is bonded to the surfacewith the pillars 2026-i. The bonding may be thermal compression,thermal/optical curing adhesive, or eutectic. In one embodiment, thefirst conductive layer 2024 may comprise varied materials. In anembodiment, part of the first conductive layer 2024 may be deposited toinclude the pillar layer 2026, and another part is part of the bondingpads 2032. For example, in the case of GaN LEDs the p-ohmic contact iscomprised of Ni and Au. In one case, layer 2026 may include both Ni andAu. In another case, the layer 2026 comprises only Ni and the pads 2032(e.g., include an Au layer at the interface). After the bonding, thepressure and heat applied to the samples will assist in diffusing theminto separate layers and create an improved ohmic contact.

The space between the pads 2032 may be filled with diverse types offiller to enhance the reliability of the bonding process. The filler mayinclude materials such as polyamide or thermally/optically annealedadhesives.

Subsequently, the device substrate 2020 may be removed, and a secondcontact layer of the device layer 2022 may be exposed. The secondcontact layer may then undergo any of the aforementioned process steps(e.g., FIGS. 8 to 10) to provide top contacts (e.g., an array of topcontact pads and/or a common electrode). Alternatively, the devicesubstrate 2020 is utilized as the common electrode.

FIG. 28 illustrates a micro device structure in which differentconductive and active layers 2022 are deposited on top of the substrate2020 followed by other conductive or blocking layers 2024. The firstconductive layer 2024 may be p-type, n-type, or intrinsic. To createpixelated devices, the conductivity of the first conductive layer(s)2024 are modulated (e.g., formed) into separate pillars of higherperformance electrical connectivity. The pillars may be smaller than(e.g., 1/10 or smaller, the pixel size such as pad 2032) whereby atleast 2 to 10, preferably 4 to 8, pillar contact each contact pad 2032.In a preferred embodiment, the pillars are between 1 nm to 100 nm wide.In one embodiment, the first conductive layer 2024 or part of the firstconductive layer 2024 may be patterned (e.g., through lithography,stamping, and other methods). In another embodiment, a very thin pillarlayer 2026 may be deposited on top of the first conductive layer 2024and annealed. The annealing process may be thermal, optical, or acombination thereof. The annealing may be done in ambient condition,vacuum, or a different gas. In one embodiment, the pillar layer 2026 maybe comprised of any one or more of ITO, gold, silver, ZnO, Ni, or othermetallic or conductive materials. The pillar layer 2026 may be depositedby a few different means, such as e-beam, thermal, or sputtering. Inaddition to the formation of pillars 2026-i, the top conductive layer2024 may also be separated (e.g., etched) into a distinct set ofconductive layer pillars 2024-i. The pillars 2026-i may act as a hardmask or a new mask may be used to etch the top conductive layer 2024 andform the conductive layer pillars 2024-i. For example, in the case ofGaN, the pillars 2026-i may be comprised of Ni, which is a natural hardmask used to etch the first conductive (e.g., p-GaN) layer 2024, to formconductive layer pillars 2024-i (e.g., using an inductively coupledplasma (ICP) etcher). The first conductive layer(s) 2024 may be etchedpartially or fully. For example, the top conductive layer(s) 2024 mayinclude both a p-layer and a blocking layer. In which case, the p-layermay be etched, and the blocking layer may be left alone.

After creating the pillars 2026-i, the substrate 2030 which includespads 2032, and may include driving circuitry, is bonded to the surfacewith the pillars 2026-l (FIG. 28D). The bonding can be thermalcompression, thermal/optical curing adhesive, or eutectic. In oneembodiment, the first conductive layer 2024 may contain variedmaterials. In this case, part of the first conductive layer 2024 may bedeposited as the pillar layer 2026 and another part may be part of thebonding pads 2032. For example, for GaN LEDs, the pillar layer 2026(e.g., p-ohmic contact) may comprise one or more of Ni and Au. In oneembodiment, the pillar layer 2026 may comprise both Ni and Au. Inanother embodiment, the pillar layer 2026 may comprise only Ni, and thepads 2032 include an Au layer at the interface. After the bonding, thepressure and heat applied to the samples will assist in diffusing theseparate layers and creating an improved ohmic contact.

With reference to FIG. 28D, in another embodiment, there may be thearray of pillars comprising redundant pillars that are not bonded to thearray of pads. For the redundant array of pillars, there may be provideda fixed voltage 2032-2 for enhancing the performance of the displays(e.g. isolating the pixels) or it can be coupled to a circuit for usingthe redundant pillars as a different function. In one case, theredundant pillars can be used as sensors. The sensor can be either animage sensor or motion sensor. In one case, the sensor can detect theeye (or hand) movement. In another case, the light from the otherpillars' pixels reflect from the eye and can be used to detect the eyemovement. In one case, another light source can be used to eliminateeyes and the sensor detects the reflection.

Subsequently, the device substrate 2020 may be removed, and a secondcontact layer of the device layer 2022 may be exposed. The secondcontact layer may then undergo any of the aforementioned process steps(e.g., FIGS. 8 to 10) to provide top contacts (e.g., an array of topcontact pads and/or a common electrode). Alternatively, the devicesubstrate 2020 is utilized as the common electrode.

With reference to FIG. 29, an alternative method includes all of theaforementioned steps from FIGS. 27 and 28, and further includes an extrapassivation layer 2028 deposited between the pillars 2024-i, on thesidewall of the pillars 2024-i, or on top of the pillars 2024-i. Thepassivation layer 2028 may comprise an ALD (e.g., dielectric) layer, aPECVD (e.g., dielectric), layer, or a polymer. The area between the pads2032 may be filled with different fillers to enhance the reliability ofthe bonding process. The fillers may be comprised of a variety ofdifferent materials, such as polyamide, or thermally/optically annealedadhesives.

Subsequently, the device substrate 2020 may be removed, and a secondcontact layer of the device layers 2022 may be exposed. The secondcontact layer may then undergo any of the aforementioned process steps(e.g., FIGS. 8 to 10) to provide top contacts (e.g., an array of topcontact pads and/or a common electrode). Alternatively, the devicesubstrate 2020 is utilized as the common electrode.

FIG. 30 illustrates an embodiment in which an extra structure (layers)2029 may be developed between the first conductive layer(s) 2024 and theactive layers of the device layers 2022. The passivation layer 2028 mayalso be deposited after the device layers 2022. The passivation layer2028 may passivate some of the defects 2029A, such as trailingdislocation. Then, the passivation layer 2028 may be either patterned(FIG. 30A) or removed from the surface (FIG. 30B). The first conductivelayer(s) 2024 may be deposited after. The passivation layer 2028 may becomprised of an ALD, PECVD, organic, or polymer layer. In anotherembodiment, a different plasma treatment, such as nitrogen, oxygen, orhydrogen plasma, may be used to create surface passivation.

According to one embodiment, an optoelectronic device may be provided.The optoelectronic device may comprising: a pad substrate comprising anarray of pads connected to a driving circuit, a device layer structuredeposited on a substrate, wherein the device layer structure including aplurality of active layers and conductive layers; and a pillar layerformed on at least a part of a first conductive layer, wherein thepillar layer is patterned into array of pillars to create pixelatedmicro devices and wherein the array of pillars is bonded to the array ofpads.

According to further embodiments, the pillars may be smaller in sizethan the pads.

According to yet further embodiments, at least a part of the firstconductive layer may be patterned. The patterning of the firstconductive layer may follow the same pattern as the patterning of thepillar layer.

According to some embodiments, the array of pillars may compriseredundant pillars that are not bonded to the array of pads. A fixedvoltage may be provided to the redundant pillars or a circuit is coupledto the redundant pillars to enhance the performance of the device. Theredundant pillars may comprise sensors one of: an image sensor or amotion sensor to detect a movement.

According to yet another embodiment, the method may further comprising apassivation layer deposited between the pillars, on the sidewall of thepillars or on top of the pillars. The passivation layer comprises one ofan ALD layer, a PECVD layer, or a polymer. The material of the pillarlayer comprises one of: ITO, gold, silver, ZnO, and Ni and a spacebetween the pads is filled with a filler material to enhance bonding.The filler material comprises polyamide or thermally/optically annealedadhesives.

According to some embodiments, the bonding between the array of pillarsand array of pads may be one of: thermal compression bonding, thermalbonding, optical bonding and eutectic bonding. A pressure or heat mayfurther be applied between the array of pillars bonded to the array ofpads to enhance bonding.

According to one embodiment, a method of fabricating an optoelectronicdevice comprising forming a device layer structure, including aplurality of active layers and conductive layers, on a substrate,forming a pillar layer on at least a part of a first conductive layer,wherein the pillar layer is patterned into array of pillars to createpixelated micro devices; and bonding a pad substrate comprising an arrayof pads connected to a driving circuit, to a top surface of the array ofpillars.

According to further embodiments, the pillars are smaller in size thanthe pads. At least a part of the first conductive layer may bepatterned. The array of pillars may comprise redundant pillars that arenot bonded to the array of pads. A fixed voltage may be provided to theredundant pillars or a circuit is coupled to the redundant pillars toenhance the performance of the device and the redundant pillars maycomprise sensors one of: an image sensor or a motion sensor to detectmovement.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and are described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of an invention as defined by theappended claims.

1. An optoelectronic device comprising: a pad substrate comprising anarray of pads connected to a driving circuit; a device layer structuredeposited on a substrate, wherein the device layer structure including aplurality of active layers and conductive layers; and a pillar layerformed on at least a part of a first conductive layer, wherein thepillar layer is patterned into an array of pillars to create pixelatedmicro devices and wherein the array of pillars is bonded to the array ofpads.
 2. The optoelectronic device of claim 1, wherein the pillars aresmaller in size than the pads.
 3. The optoelectronic device of claim 1,wherein the part of the first conductive layer is patterned.
 4. Theoptoelectronic device of claim 3, wherein the patterning of the firstconductive layer follows the same pattern as the patterning of thepillar layer.
 5. The optoelectronic device of claim 1, wherein the arrayof pillars comprise redundant pillars that are not bonded to the arrayof pads.
 6. The optoelectronic device of claim 5, wherein a fixedvoltage is provided to the redundant pillars or a circuit is coupled tothe redundant pillars to enhance the performance of the device.
 7. Theoptoelectronic device of claim 5, wherein redundant pillars comprisesensors one of: an image sensor or a motion sensor to detect a movement.8. The optoelectronic device of claim 1, further comprising apassivation layer deposited between the pillars, on the sidewall of thepillars or on top of the pillars.
 9. The optoelectronic device of claim1, wherein the passivation layer comprises one of an ALD layer, a PECVDlayer, or a polymer.
 10. The optoelectronic device of claim 2, wherein amaterial of the pillar layer comprises one of: ITO, gold, silver, ZnO,and Ni.
 11. The optoelectronic device of claim 1, wherein a spacebetween the pads is filled with a filler material to enhance bonding.12. The optoelectronic device of claim 11, wherein the filler materialcomprises polyamide or thermally/optically annealed adhesives.
 13. Theoptoelectronic device of claim 1, wherein the bonding between the arrayof pillars and array of pads is one of: thermal compression bonding,thermal bonding, optical bonding and eutectic bonding.
 14. Theoptoelectronic device of claim 1, wherein a pressure or heat is furtherapplied between the array of pillars bonded to the array of pads toenhance bonding.
 15. A method of fabricating an optoelectronic devicecomprising: forming a device layer structure, including a plurality ofactive layers and conductive layers, on a substrate; forming a pillarlayer on at least a part of a first conductive layer, wherein the pillarlayer is patterned into array of pillars to create pixelated microdevices; and bonding a pad substrate comprising an array of padsconnected to a driving circuit, to a top surface of the array ofpillars.
 16. The method of claim 15, wherein the pillars are smaller insize than the pads.
 17. The method of claim 15, wherein the at least apart of the first conductive layer is patterned.
 18. The method of claim15, wherein the array of pillars comprise redundant pillars that are notbonded to the array of pads.
 19. The method of claim 15, wherein a fixedvoltage is provided to the redundant pillars or a circuit is coupled tothe redundant pillars to enhance the performance of the device.
 20. Themethod of claim 15, wherein the redundant pillars comprise sensors oneof: an image sensor or a motion sensor to detect a movement.